Electroric device, integrated circuit, and method of manufacturing the same

ABSTRACT

The present invention provides an electronic device including a transporting layer which involves a low environmental load and which is excellent in semiconductor characteristics by means of a configuration having, on the surface of a base body, at least a transporting layer constituted by a carbon nanotube structure layer having a network structure in which a plurality of carbon nanotubes mutually cross-link. Also, provided is a method of manufacturing the same.

TECHNICAL FIELD

The present invention relates to an electronic device using a carbonnanotube structure as a transporting layer, an integrated circuit usingthe electronic device, and a method of manufacturing the same.

BACKGROUND ART

Carbon nanotubes (CNTs), with their unique shapes and characteristics,are being considered for various applications. A carbon nanotube has atubular shape of one-dimensional nature which is obtained by rolling oneor more graphene sheets composed of six-membered rings of carbon atomsinto a tube. A carbon nanotube which is formed from one graphene sheetis called a single-wall nanotube (SWNT), while a carbon nanotube whichis formed from multiple graphene sheets is called a multi-wall nanotube(MWNT). SWNTs are about 1 nm in diameter, while multi-wall carbonnanotubes measure several tens nm in diameter, and both are far thinnerthan their predecessors, which are called carbon fibers.

One of the characteristics of carbon nanotubes resides in that theaspect ratio of length to diameter is very large since the length ofcarbon nanotubes is on the order of micrometers. Carbon nanotubes areunique in their extremely rare nature of being both metallic andsemiconductive because six-membered rings of carbon atoms in carbonnanotubes are arranged into a spiral. In addition, the electricconductivity of carbon nanotubes is very high and allows a current flowat a current density of 100 MA/cm² or more.

Carbon nanotubes excel not only in electrical characteristics but alsoin mechanical characteristics. That is, the carbon nanotubes aredistinctively tough, as attested by their Young's moduli exceeding 1TPa, which belies their extreme lightness resulting from being formedsolely of carbon atoms. In addition, the carbon nanotubes have highelasticity and resiliency resulting from their cage structure. Havingsuch various and excellent characteristics, carbon nanotubes are veryappealing as industrial materials.

Applied researches that exploit the excellent characteristics of carbonnanotubes have been heretofore made extensively. To give a few examples,a carbon nanotube is added as a resin reinforcer or as a conductivecomposite material, while another research utilizes a carbon nanotube asa probe of a scanning probe microscope. Carbon nanotubes have also beenutilized as minute electron sources, field emission electronic devices,and flat displays. An application that is being developed is to use as ahydrogen storage a carbon nanotube.

In association with a recent increase in speed of information processingor communication, an electrical signal with a frequency equal to orhigher than a frequency that can be processed by means of a transistorusing silicon or gallium arsenide currently used must be controlled oramplified. In addition, a substance applying a large load to theenvironment may be used for an electronic device itself produced byusing silicon, gallium arsenide, or the like, or may be used in aproduction step of the device. In view of the above, a carbon nanotubewhich is composed of carbon applying a small load to the environment andis considered to operate at a frequency higher than those of silicon andgallium arsenide has been attracting attention, and an electronic devicesuch as a transistor has been prototyped by using the carbon nanotube.However, a handling technique on the order of nanometer is necessary toput an electronic device using a carbon nanotube such as that describedabove into practical use.

For example, JP-A 2003-17508 discloses a field effect transistorconstituted by arranging a plurality of carbon nanotubes in parallelbetween source and drain electrodes. In the method of arranging thosecarbon nanotubes, a self-organizing molecular membrane is used and thechargeability of the molecular membrane is made to differ from site tosite, whereby a carbon nanotube having property of being negativelycharged can be arranged at an arbitrary position. However, a carbonnanotube is a very thin fibrous material. Even if part of the carbonnanotube adsorbs to an area showing positive chargeability, the carbonnanotube is not necessarily arranged to connect the source and thedrain. Therefore, the carbon nanotube may be connected to only one ofthem or may be arranged between the electrodes without connecting them,which is too uncertain. Alternatively, a photo tweezer method or anorientation method by means of an electric field are disclosed, butthese methods are not different from the above method in that theconnection occurs only by chance, and hence are insufficient astechniques for integration.

Meanwhile, an attempt has been made, which includes: dispersing a carbonnanotube into a liquid; applying and depositing the dispersion onto asubstrate; and using the applied film as a transporting layer (channel).For example, “Random networks of carbon nanotubes as an electronicmaterial”, written by E. S. Snow, J. P. Novak, P. M. Campbell, and D.Park, APPLIED PHYSICS LETTERS (U.S.A.), 2003, Vol. 82, No. 13, p. 2145to p. 2147 reports that a liquid into which single-wall carbon nanotubesare dispersed at a high density is applied, whereby many connections aremade to connect the carbon nanotubes, and thus the applied liquid can beused for a thin film transistor. In a mere dispersion film, anelectrical pulse may occur somewhere if a channel has a large area, butthe probability of the occurrence reduces as the channel is thinned, sohigh density is hardly obtained. Furthermore, for performing thinningand integration, an excessive nanotube must be cut and removed because atip of a long carbon nanotube lying off the area may establish a shortcircuit with other device or wiring. However, it is extremely difficultto pattern a deposit in a contact state, and carbon nanotubes scatterduring an etching operation, so patterning is impossible in fact. Inaddition, the deposit is merely in contact, so there arises a drawbackin that the resultant device is unstable and the current fluctuates inassociation with vibration or application of a voltage.

An approach to solving the drawback of the applied film due to contactof a carbon nanotube is, for example, a method involving: dispersing acarbon nanotube in a resin; and solidifying or applying the dispersion.For example, JP-A 2003-96313 discloses a method of manufacturing a thinfilm transistor by using a composite obtained by dispersing carbonnanotubes into a polymer. However, contact between carbon nanotubeshardly occurs owing to the presence of the resin, thereby leading to aproblem in terms of electrical contact. In addition, the density ofcarbon nanotubes reduces owing to the presence of the resin, so thenumber of electrical paths reduces, thereby making it difficult to usethe device as an electronic device. If a mixing amount of carbonnanotubes is increased to solve this, an amount of binders reduces, withthe result that the strength of the dispersion film itself reduces andthe same problem as that of the above deposit film occurs.

Therefore, an object of the present invention is to solve the problemsin the prior art. More specifically, an object of the present inventionis to provide: an electronic device capable of stably obtainingcharacteristics of a carbon nanotube; and a manufacturing method withwhich a uniform electronic device can be stably obtained.

DISCLOSURE OF THE INVENTION

The above object is achieved by the present invention described below.

That is, according to one aspect of the present invention, there isprovided an electronic device, characterized by including: three or moreelectrodes; and a transporting layer constituted by a carbon nanotubestructure formed into a network structure by a plurality of carbonnanotubes and cross-linked sites each constituted by chemical bonding ofthe different carbon nanotubes, in which a carrier is transported inaccordance with a voltage applied to the electrodes.

In the electronic device of the present invention, a carbon nanotubestructure formed into a network structure by a plurality of carbonnanotubes and cross-linked sites in each of which the different carbonnanotubes cross-link through chemical bonding is used as a transportinglayer. Therefore, as compared to the case where a mere carbon nanotubedispersion film is used as the transporting layer, a phenomenon does notoccur in which an electrical path is lost or fluctuates owing to theinstability of the contact state and arrangement state of carbonnanotubes. As a result, the device can be allowed to stably operate asan electronic device. The term “electrical path” refers to a conductionpath of a carrier (hole, electron) to be transported in the transportinglayer. In addition, in the electrical path, a carrier is not necessarilyconducted in a cross-linked site. The transmission of a carrier may beperformed by virtue of a tunnel effect or the like when a cross-linkedsite is sufficiently short. A clear theory has not been established yetfor the principle of carrier transmission not only in a carbon nanotubestructure with a network structure but also a carbon nanotubedispersion. Therefore, future research may enable the principle to beexplained with improved validity. It is apparent, however, that thosefacts do not negate the effectiveness of the electronic device obtainedby the structure of the present invention.

Next, the electronic device of the present invention includes three ormore electrodes. In particular, it is preferable to constitute theelectrodes as the source, drain, and gate electrodes of a field effecttransistor. More than three electrodes may be arranged. For example, aplurality of gate electrodes may be arranged. In addition, a gateelectrode may be arranged above or below the transporting layer. Thegate electrode is not necessarily formed into a planar shape, and may beformed into a three-dimensional shape to cover the transporting layer tothereby enhance the action of a gate voltage.

A field effect transistor having a MOS-FET (metal oxide semiconductorfield effect transistor) structure is effective in constituting a highlyintegrated device because operating power can be reduced and switchingcharacteristics become good.

In addition, a field effect transistor having a MES-FET (metalsemiconductor field effect transistor) structure is effective inperforming a switching operation at a high speed. In particular, in thecase where a carbon nanotube structure is used as the transportinglayer, a switching speed can be increased because a carbon nanotube hasa high carrier transporting speed.

The carbon nanotube structure has a network structure in whichcross-linked sites are connected with a carbon nanotube. The carbonnanotube is preferably a single-wall carbon nanotube because intrinsicsemiconductor characteristics can be easily exploited.

In the case where the carbon nanotubes are mainly multi-wall carbonnanotubes, a graphene sheet structure on a surface layer is partlydestroyed when a cross-linked site binds to a carbon nanotube. However,such a case is preferable in that another graphene sheet layer is formedat the center and an electrical path is easily formed without therupture of the carbon nanotube structure. Multi-wall carbon nanotubesare not limited to merely completely concentric and cylindrical ones,and include tubes whose vertical cross section taken along their centeraxis has a multilayer structure such as so-called cup-stacked carbonnanotubes.

The term “mainly” refers to which one of a component ratio ofsingle-wall carbon nanotubes and a component ratio of multi-wall carbonnanotubes is larger than the other. In general, in most cases, one ofthe component ratio of single-wall carbon nanotubes and the componentratio of multi-wall carbon nanotubes is overwhelmingly large as comparedto the other in accordance with a manufacturing method of a carbonnanotube. Since such carbon nanotubes are supplied to the market whilesingle-wall and multi-wall carbon nanotubes are distinguished from eachother, one of the single-wall and multi-wall carbon nanotubes can beselected and used in producing the electronic device of the presentinvention. In addition, the single-wall and multi-wall carbon nanotubesmay be intentionally mixed and used.

By the way, a multi-wall carbon nanotube, unlike a single-wall carbonnanotube, is said to have electrical characteristics similar to those ofa metal. It has become clear that the carbon nanotube structure of thepresent invention in which a cross-linked site is formed operates alsoas a transporting layer. Although the reason for this is unclear, theresult will be shown in Examples below. The cross-linked site presumablyacts as a structure like a Schottky barrier, but the validity of thispresumption is unclear. However, it has been found that a transportinglayer is formed by using a multi-wall carbon nanotube which can beproduced with high purity and in a large amount as compared to asingle-wall carbon nanotube and which can be easily handled. As aresult, it becomes extremely easy to industrially produce applied activedevices of carbon nanotubes in large amounts.

A chemical bond constituting a cross-linked site is preferably achemical structure selected from the group consisting of —COO(CH₂)₂OCO—,—COOCH₂CHOHCH₂OCO—, —COOCH₂CH(OCO—)CH₂OH—, —COOCH₂CH(OCO—)CH₂OCO—, and—COO—C₆H₄—COO—. Each of those bonds is an extremely short structure ascompared to the length of a carbon nanotube. Therefore, a distancebetween carbon nanotubes at a cross-linked site can be made extremelyshort. As a result, the density of carbon nanotubes in a carbon nanotubestructure can be increased, thereby facilitating the formation of anelectrical path. As a result, even if the size of the transporting layerbecomes small, the device can be allowed to stably operate as anelectronic device. Alternatively, the amount of a current that can bepassed through the transporting layer can be increased. In particular,in the case where —COO—C₆H₄—COO— is adopted as the structure of thecross-linked site, electrical characteristics are stable, which ispreferable in that deterioration with time is suppressed.

The chemical bond constituting the cross-linked site is also preferablyone selected from the group consisting of —COOCO—, —O—, —NHCO—, —COO—,—NCH—, —NH—, —S—, —O—, —NHCOO—, and —S—S— because of the same reason asthat described in the above paragraph.

The carbon nanotube structure is preferably obtained by using a solutioncontaining a plurality of carbon nanotubes to which functional groupsare bonded, to thereby form a cross-linked site through chemical bondingof the functional groups connected to the carbon nanotubes.

By using carbon nanotubes to which functional groups are bonded inadvance, the amount of cross-linking is controlled and the density ofnanotubes and the amount of cross-linked sites formed in the carbonnanotube structure can be uniformized. As a result, even in case ofintegration, large variations in characteristics of an electronic devicedue to the position of the carbon nanotube structure can be reduced. Ifa chemical bond to directly cross-link separated nanotubes is allowed tooccur for forming a network-like carbon nanotube structure, the carbonnanotubes hardly cross-link or the graphene sheet structure on thenanotube surface is entirely destroyed because the stability of thesurface of a carbon nanotube is extremely high. Therefore, it is hard toobtain a desired network structure.

In a carbon nanotube structure, a cross-linked site is more preferablyformed by curing a solution containing carbon nanotubes havingfunctional groups and a cross-linking agent that prompts a cross-linkingreaction with the functional groups, to prompt a cross-linking reactionbetween each of the functional groups bonded to different carbonnanotubes and the cross-linking agent. Combination of a functional groupcausing cross-linking and a cross-linking agent can be selected, so achemical bond constituting a cross-linked site can be of a desiredstructure, and an electronic device having desired characteristics canbe obtained.

Furthermore, the cross-linking agent is preferably anon-self-polymerizable cross-linking agent.

If the cross-linking agent has its property of polymerizing with othercross-linking agents (self-polymerizability), the connecting group maycontain a polymer in which two or more cross-linking agents areconnected, thereby reducing an actual density of the carbon nanotubes inthe carbon nanotube structure. Therefore, the transporting layer may beunable to exert sufficient semiconductivity.

On the other hand, when the cross-linking agent is anon-self-polymerizable cross-linking agent, a gap between carbonnanotubes can be controlled to the size of a product as a result of thecross-linking reaction between a functional group and a cross-linkingagent used. Therefore, a desired network structure of carbon nanotubescan be obtained with high duplicability. Further, reducing the size ofthe residue after the reaction of the cross-linking agent can extremelynarrow a gap between carbon nanotubes electrically and physically. Inaddition, carbon nanotubes in the structure can be densely structured.Therefore, a fine electronic device can be formed, or the amount of acurrent that can be passed through the transporting layer can beincreased.

In the present invention, the term “self-polymerizable” refers toproperty with which the cross-linking agents may prompt a polymerizationreaction with each other in the presence of other components such aswater or in the absence of other components. On the other hand, the term“not self-polymerizable” means that the cross-linking agent has no suchproperty.

Examples of the functional groups include —OH, —COOH, —COOR (where Rrepresents a substituted or unsubstituted hydrocarbon group), —COX(where X represents a halogen atom), —NH₂, and —NCO. A selection of atleast one functional group from the group consisting of the abovefunctional groups is preferable, and in such a case, a cross-linkingagent, which may prompt a cross-linking reaction with the selectedfunctional group, is selected as the cross-linking agent.

Further, examples of the preferable cross-linking agent include apolyol, a polyamine, a polycarboxylic acid, a polycarboxylate, apolycarboxylic acid halide, a polycarbodiimide, a polyisocyanate, andhydroquinone. A selection of at least one cross-linking agent from thegroup consisting of the above cross-linking agents is preferable, and insuch a case, a functional group, which may prompt a cross-linkingreaction with the selected cross-linking agent, is selected as thefunctional group.

At least one functional group and at least one cross-linking agent arepreferably selected respectively from the group consisting of thefunctional groups exemplified as the preferable functional groups andthe group consisting of the cross-linking agents exemplified as thepreferable cross-linking agents, so combination of the functional groupand the cross-linking agent may prompt a cross-linking reaction witheach other.

Examples of the particularly preferable functional group include —COOR(where R represents a substituted or unsubstituted hydrocarbon group).Introduction of a carboxyl group into carbon nanotubes is relativelyeasy, and the resultant substance (carbon nanotube carboxylic acid) hashigh reactivity. Therefore, after the formation of the substance, it isrelatively easy to esterify the substance to convert its functionalgroup into —COOR (where R represents a substituted or unsubstitutedhydrocarbon group). The functional group easily prompts a cross-linkingreaction and is suitable for formation of an applied film.

A polyol can be exemplified as the cross-linking agent corresponding tothe functional group. A polyol is cured by a reaction with -COOR (whereR represents a substituted or unsubstituted hydrocarbon group), andforms a robust cross-linked substance with ease. Among polyols, each ofglycerin and ethylene glycol reacts with the above functional groupswell. Moreover, each of glycerin and ethylene glycol itself is highlybiodegradable, and provides a low environmental load.

A second preferable structure of the cross-linked site is formed bychemical bonding of the functional groups. In this case, functionalgroups connected in advance to carbon nanotubes are bonded. Therefore,the resultant electronic device using a carbon nanotube structure hasdesired characteristics. In addition, the density of the carbon nanotubestructure can be increased as compared to the case where a cross-linkingagent is interposed between functional groups.

A reaction for chemically bonding functional groups is preferably oneselected from dehydration condensation, a substitution reaction, anaddition reaction, and an oxidation reaction.

In the electronic device of the present invention, in the case where thecarbon nanotube structure is patterned into a shape corresponding to aformation area of the transporting layer, carbon nanotubes arechemically bonded at a cross-linked site. Therefore, no electrical pathin the pattern is lost, and a stable operation can be achieved.Furthermore, the carbon nanotube structure formed into a networkstructure by cross-linked sites in each of which carbon nanotubescross-link through chemical bonding, unlike a carbon nanotube dispersionfilm due to accidental contact, entirely forms a uniform structure.Therefore, variations in characteristics of the transporting layer dueto the position of the carbon nanotube structure before the patterningare small, and variations in characteristics of the electronic deviceafter the patterning are reduced.

In addition, when an electronic device having, as a transporting layer,a carbon nanotube structure formed into a network structure bycross-linked sites in each of which carbon nanotubes cross-link throughchemical bonding is formed on a flexible substrate, variations incharacteristics caused by a change of an electrical path involvingdeformation such as bending of a substrate, which cannot be avoided in aconventional electronic device having a transporting layer in whichcarbon nanotubes mutually contact, are reduced.

In addition, in the electronic device of the present invention, anelectrical path in the structure is homogeneously formed. Therefore,even in the case where the device is formed as an integrated circuit ona substrate, an integrated circuit in which variations incharacteristics of each device are small can be obtained.

According to another aspect of the present invention, there is provideda method of manufacturing an electronic device that includes, on a basebody, three or more electrodes and a transporting layer in which acarrier is transported in accordance with a voltage applied to theelectrodes, the method being characterized by including: a supplyingstep of supplying the base body with a solution containing a pluralityof carbon nanotubes to which functional groups are bonded; and across-linking step of chemically bonding the functional groups togetherto construct a network structure in which the carbon nanotubes mutuallycross-link, thereby forming a carbon nanotube structure used as thetransporting layer.

In the present invention, in the supplying step of supplying a base bodysurface with a solution containing carbon nanotubes having functionalgroups (hereinafter, the solution may be referred to as a “cross-linkingapplication solution”), the entire surface or part of the surface of thebase body, or an inside or the like of a desired mold is supplied withthe cross-linking application solution. Then, in the subsequentcross-linking step, the functional groups are chemically bonded togetherto construct a network structure in which the carbon nanotubes mutuallycross-link, thereby forming a carbon nanotube structure. Then, thecarbon nanotube structure layer is used as the transporting layer.Through those two steps, the structure itself of the carbon nanotubestructure layer is stabilized on the base body surface.

If the supplying step includes an applying step of applying the solutiononto the base body, and the carbon nanotube structure is of a filmshape, a layered carbon nanotube structure having a network structurecan be obtained. As described later, the structure can be patternedreadily into a desired shape. This case is preferable in forming athin-layer device.

The carbon nanotubes to be used in the method of the present inventionare preferably single-wall carbon nanotubes because intrinsicsemiconductor characteristics can be easily exploited.

In the case where the carbon nanotubes are mainly multi-wall carbonnanotubes, as described in the electronic device, it has been found thata transporting layer is formed by using a multi-wall carbon nanotubewhich can be produced with high purity and in a large amount as comparedto a single-wall carbon nanotube and which can be easily handled. Thisfinding is extremely useful in industrially producing applied activedevices of carbon nanotubes in large amounts.

The term “mainly” refers to which one of a component ratio ofsingle-wall carbon nanotubes and a component ratio of multi-wall carbonnanotubes used for producing a carbon nanotube structure is larger thanthe other. In general, in most cases, one of the component ratio ofsingle-wall carbon nanotubes and the component ratio of multi-wallcarbon nanotubes is overwhelmingly large as compared to the other inaccordance with a manufacturing method of a carbon nanotube. Therefore,it is only necessary to select one of the single-wall and multi-wallcarbon nanotubes. However, the single-wall and multi-wall carbonnanotubes also may be intentionally mixed and used.

In addition, a top-down integrated circuit can be easily produced bycombination with the formation of a transporting layer throughpatterning of a carbon nanotube structure to be described later.

A preferable first method of forming a cross-linked site in the methodof manufacturing an electronic device of the present invention is amethod involving incorporating a cross-linking agent for cross-linkingthe functional groups in the solution. Since the combination of afunctional group and a cross-linking agent which cross-links thefunctional group is determined, unlike a carbon nanotube dispersionfilm, it becomes possible to ensure that the formation of cross-linkingoccurs.

In addition, a non-self-polymerizable cross-linking agent is preferablyused as the cross-linking agent. When a self-polymerizable cross-linkingagent is used as the cross-linking agent, and cross-linking agentsprompt a polymerization reaction with each other during or prior to thecross-linking reaction in the cross-linking step, bonding between thecross-linking agents is enlarged and lengthened. As a result, a gapitself between carbon nanotubes to be bonded to the agents may beinevitably large. At this time, since it is in fact difficult to controlthe degree of the reaction due to the self-polymerizability between thecross-linking agents, a cross-linking structure between carbon nanotubesin the structure may vary in accordance with a variation in apolymerization state between the cross-linking agents.

However, when a non-self-polymerizable cross-linking agent is used,cross-linking agents do not mutually polymerize at least during andprior to the cross-linking step. In addition, in the cross-linked sitebetween the carbon nanotubes, only a residue by one cross-linkingreaction of the cross-linking agent is interposed as a connecting groupbetween residues of the functional groups remaining after thecross-linking reaction. As a result, the characteristics of theresultant carbon nanotube structure layer are entirely uniformized. Evenwhen the layer is patterned in a patterning step, variations incharacteristics of the carbon nanotube structure layer after thepatterning can be significantly reduced.

The functional groups are preferably at least one group selected fromthe group consisting of —OH, —COOH, —COOR (where R represents asubstituted or unsubstituted hydrocarbon group), —COX (where Xrepresents a halogen atom), —NH₂, and —NCO from the viewpoint of theease with which carbon nanotubes bind to functional groups.

Further, the cross-linking agents are preferably at least onecross-linking agent selected from the group consisting of a polyol, apolyamine, a polycarboxylic acid, a polycarboxylate, a polycarboxylicacid halide, a polycarbodiimide, a polyisocyanate, and hydroquinonebecause the size of a cross-linked site can be reduced to an appropriateone. If the size of a cross-linking agent is excessively large, carbonnanotubes are substantially isolated from each other, and the effect ofconnection at the cross-linked site is hardly obtained.

The functional groups are particularly preferably —COOR (where Rrepresents a substituted or unsubstituted hydrocarbon group) from theviewpoint of the ease with which carbon nanotubes bind to functionalgroups. At this time, the cross-linking agents are preferably polyols,more preferably glycerin and/or ethylene glycol from the viewpoints ofthe ease with which a non-self-polymerizable cross-linking agent and—COOR prompt a cross-linking reaction as described above, the ease withwhich an applied film is formed, high biodegradability, and a lowenvironmental load.

In addition, when the cross-linking agents do not mutually cross-link,or differ from each other in reactivity with respect to the functionalgroups bonded to the carbon nanotubes, a gap between carbon nanotubescan be controlled even if multiple kinds of non-self-polymerizablecross-linking agents are mixed to cross-link carbon nanotubes. As aresult, a similar reducing effect on variations can be obtained. On theother hand, in the case where cross-linking is performed by usingcross-linking agents different in a stepwise manner, if cross-linking isperformed by using a non-self-polymerizable cross-linking agent at aninitial cross-linking stage, the skeleton of a network structure of thecarbon nanotube is complete in a state where a distance between carbonnanotubes is controlled. Therefore, a self-polymerizable cross-linkingagent or a cross-linking agent that cross-links the initialcross-linking agent (or a residue thereof) may be used in the subsequentcross-linking step.

In the method of manufacturing an electronic device of the presentinvention, a solvent may be additionally incorporated in the solution tobe used in the applying step. The cross-linking agent may serve also asthe solvent depending on the kind of the cross-linking agent.

A preferable second method of forming a cross-linked site in the methodof manufacturing an electronic device of the present invention is amethod involving chemically bonding the functional groups together.

By doing so, the structure of the cross-linked site is determined byfunctional groups bonded in advance to carbon nanotubes. Therefore, thesize of the cross-linked site for bonding the carbon nanotubes togetherbecomes constant. Since a carbon nanotube has an extremely stablechemical structure, there is a low possibility that functional groupsand the like other than a functional group to modify the carbon nanotubeare bonded to the carbon nanotube. In the case where the functionalgroups are chemically bonded together, the designed structure of thecross-linked site can be obtained, thereby providing a homogeneouscarbon nanotube structure.

Furthermore, the functional groups are chemically bonded together, sothe length of the cross-linked site between the carbon nanotubes can beshorter than that in the case where the functional groups arecross-linked together with a cross-linking agent interposedtherebetween. Therefore, the carbon nanotube structure is dense, and canbe easily made homogeneous.

A reaction for chemically bonding the functional groups together isparticularly preferably condensation, a substitution reaction, anaddition reaction, or an oxidation reaction.

In the method of manufacturing an electronic device of the presentinvention, the functional groups are preferably: at least one selectedfrom the group consisting of —COOR (where R represents a substituted orunsubstituted hydrocarbon group), —COOH, —COX (where X represents ahalogen atom), —OH, —CHO, and —NH₂ for a condensation reaction; at leastone selected from the group consisting of —NH₂, —X (where X represents ahalogen atom), —SH, —OH, —OSO₂CH₃, and —OSO₂(C₆H₄)CH₃ for a substitutionreaction; at least one selected from the group consisting of —OH and—NCO for an addition reaction; and —SH for an oxidation reaction.

In particular, in the electronic device of the present invention,molecules containing the above functional groups may be bonded to carbonnanotubes and chemically bonded at functional group portions listedabove to construct a cross-linked site.

Examples of the functional groups particularly preferable for use in thecondensation reaction include —COOH. Introduction of a carboxyl groupinto carbon nanotubes is relatively easy, and the resultant substance(carbon nanotube carboxylic acid) has high reactivity. Therefore,functional groups for forming a network structure can be easilyintroduced into multiple sites of one carbon nanotube. Moreover, thefunctional groups are suitable for formation of an applied film becausethe functional groups easily prompt a condensation reaction.

In addition, a solution for producing the carbon nanotube structure ofthe present invention is characterized by containing: a plurality ofcarbon nanotubes each having functional groups; and an additive forbonding the functional groups of the different carbon nanotubestogether.

A network-like and homogeneous carbon nanotube structure can be producedwith extreme ease of handling by using the solution of the presentinvention. It is essential to use a condensation agent as the additivewhen a condensation reaction is adopted or to use a base as the additivewhen a substitution reaction is adopted. An oxidation reactionaccelerator is desirably used as the additive when an oxidation reactionis adopted. In addition, a reaction accelerator or the like is notalways needed in an addition reaction. The additive may be mixed withthe solution in advance or may be mixed immediately before use.

In the method of manufacturing an electronic device of the presentinvention, the carbon nanotube structure layer is more preferablypatterned into a shape corresponding to the transporting layer toprovide for a patterning step. In this stage, the structure itself ofthe carbon nanotube structure layer has already been stabilized in theabove cross-linking step. Since patterning is performed in this state,such inconvenience as scattering of a carbon nanotube in the patterningstep may not occur, so the layer can be patterned into a patterncorresponding to the transporting layer. In addition, the carbonnanotube structure layer itself is structured, so connection between thecarbon nanotubes is surely ensured and an electrical path can be stablyformed. In addition, in the carbon nanotube structure, a plurality offunctional groups are chemically bonded together to mutually cross-linka plurality of carbon nanotubes together. As a result, a cross-linkedsite can be uniformly formed in the entire structure without dependenceon accidental contact unlike the carbon nanotube dispersion film.Therefore, even after a large carbon nanotube structure after undergoingthe cross-linking step is patterned into a smaller size, an electricalpath can be stably ensured, and a homogeneous electronic device can beformed.

Each of the following two modes A and B can be given as the patterningstep.

A: A mode in which the patterning step is a step involving: subjecting acarbon nanotube structure layer in a region having a pattern other thana pattern corresponding to the transporting layer on the base bodysurface to dry etching to remove the carbon nanotube structure layer inthe region; and patterning the carbon nanotube structure layer into thepattern corresponding to the transporting layer.

A mode can be given as an operation of patterning the carbon nanotubestructure layer into the pattern corresponding to the transportinglayer, in which the patterning step is further divided into two steps: aresist layer forming step of forming a resist layer (preferably a resinlayer) on the carbon nanotube structure layer in the region having thepattern corresponding to the transporting layer on the base bodysurface, and a removing step of removing a carbon nanotube structurelayer exposed in a region other than the region by subjecting a surfaceof the base body on which the carbon nanotube structure layer and theresist layer are laminated to dry etching (preferably by irradiating thesurface with a radical of an oxygen molecule which can be generated byirradiating the oxygen molecule with ultraviolet light to be used). Inthis case, subsequent to the removing step, a resist layer peeling-offstep of peeling off the resist layer formed in the resist layer formingstep is further included. As a result, the patterned carbon nanotubestructure layer can be exposed.

In addition, in the mode described above, a mode can be given as theoperation of patterning the carbon nanotube structure layer into thepattern corresponding to the transporting layer, in which the carbonnanotube structure layer in the region having a pattern other than thepattern corresponding to the transporting layer on the base body surfaceis selectively irradiated with an ion of a gas molecule in the form ofan ion beam to remove the carbon nanotube structure layer in the regionthereby patterning the carbon nanotube structure layer into the patterncorresponding to the transporting layer.

B: A mode in which the patterning step is a step including:

a resist layer forming step of forming a resist layer on the carbonnanotube structure layer in the region having the pattern correspondingto the transporting layer on the base body surface; and

a removing step of removing a carbon nanotube structure layer exposed ina region other than the region by bringing a surface of the base body onwhich the carbon nanotube structure layer and the resist layer arelaminated into contact with an etchant.

In the method of manufacturing an electronic device of the presentinvention, when 3 electrodes are arranged in a carbon nanotube structurehaving a network structure in which carbon nanotubes are chemicallybonded to form cross-linked sites, and one of the electrodes is used asa control electrode, it has been found that not only a single-wallcarbon nanotube but also a multi-wall carbon nanotube having highproductivity and high availability exhibits characteristics similar tothose of a semiconductor device. This carbon nanotube is patterned afterit has been structured into a network shape that can be stablypatterned. As a result, high density patterning, which has beendifficult in a contact state, can be performed without reliance onaccidental contact between carbon nanotubes. Therefore, the method ofmanufacturing an electronic device of the present invention is amanufacturing method which is extremely excellent in productivity ascompared to a conventional approach and which is suitable for forming atop-down integrated circuit because an electronic device can beassuredly and effectively obtained with the method of the presentinvention. The method of manufacturing an electronic device of thepresent invention provides an extremely revolutionary method forembodying a highly integrated device using a carbon nanotube which hasbeen currently promising.

As described above, according to the present invention, there can beprovided an electronic device and an integrated circuit each havingstable electrical characteristics. Furthermore, a uniform electronicdevice using a carbon nanotube can be produced with extreme efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional diagram of a MOS-FET carbon nanotubefield effect transistor according to an embodiment of the presentinvention.

FIG. 2 is a schematic diagram of the MOS-FET carbon nanotube fieldeffect transistor shown in FIG. 1 when viewed from the above.

FIG. 3 is a schematic sectional diagram of a MES-FET carbon nanotubefield effect transistor according to an embodiment of the presentinvention.

FIG. 4(1) is a schematic sectional diagram of the surface of a base bodyshowing a state during a manufacturing process for explaining an exampleof a method of manufacturing an electronic device of the presentinvention, showing a state where nothing is formed on the substrate.

FIG. 4(2) is a schematic sectional diagram of the surface of the basebody showing a state during the manufacturing process for explaining theexample of the method of manufacturing an electronic device of thepresent invention, showing a state where a gate electrode has beenformed on the substrate.

FIG. 4(3) is a schematic sectional diagram of the surface of the basebody showing a state during the manufacturing process for explaining theexample of the method of manufacturing an electronic device of thepresent invention, showing a state where a gate insulating film has beenformed on the substrate.

FIG. 4(4) is a schematic sectional diagram of the surface of the basebody showing a state during the manufacturing process for explaining theexample of the method of manufacturing an electronic device of thepresent invention, showing a state after a supplying step.

FIG. 4(5) is a schematic sectional diagram of the surface of the basebody showing a state during the manufacturing process for explaining theexample of the method of manufacturing an electronic device of thepresent invention, showing a state after a cross-linking step.

FIG. 5(6) is a schematic sectional diagram of the surface of the basebody showing a state during the manufacturing process for explaining theexample of the method of manufacturing an electronic device of thepresent invention, showing a state where a resist layer has been formedon the entire surface with a carbon nanotube structure layer formed,during a patterning step after the steps shown in FIGS. 4.

FIG. 5(7) is a schematic sectional diagram of the surface of the basebody showing a state during the manufacturing process for explaining theexample of the method of manufacturing an electronic device of thepresent invention, showing a state of the substrate after undergoing aresist layer forming step, during the patterning step after the stepsshown in FIGS. 4.

FIG. 5(8) is a schematic sectional diagram of the surface of the basebody showing a state during the manufacturing process for explaining theexample of the method of manufacturing an electronic device of thepresent invention, showing a state of the substrate after undergoing aremoving step, during the patterning step after the steps shown in FIGS.4.

FIG. 5(9) is a schematic sectional diagram of the surface of the basebody showing a state during the manufacturing process for explaining theexample of the method of manufacturing an electronic device of thepresent invention, showing a state of the substrate after undergoing aresist layer peeling-off step, during the patterning step after thesteps shown in FIGS. 4.

FIG. 5(10) is a schematic sectional diagram of the surface of the basebody showing a state during the manufacturing process for explaining theexample of the method of manufacturing an electronic device of thepresent invention, showing a state of the substrate after undergoing astep of forming source and drain electrodes.

FIG. 6 is a reaction scheme for the synthesis of a carbon nanotubecarboxylic acid in (Addition Step) of Example 1.

FIG. 7 is a reaction scheme for esterification in (Addition Step) ofExample 1.

FIG. 8 is a reaction scheme for cross-linking by an ester exchangereaction in (Cross-linking Step) of Example 1.

FIG. 9 is a reaction scheme for cross-linking by an ester exchangereaction in (Cross-linking Step) of Example 3.

FIG. 10 is a graph showing a change in conductance between a source anda drain with a gate voltage in an electronic device using a carbonnanotube structure constituted by a single-wall carbon nanotube producedin Example 1 and glycerin.

FIG. 11 is a graph showing a change in conductance between a source anda drain with a gate voltage in an electronic device using a carbonnanotube structure constituted by a single-wall carbon nanotube producedin Example 2 and glycerin.

FIG. 12 is a graph showing a change in conductance between a source anda drain with a gate voltage in an electronic device using a carbonnanotube structure constituted by a multi-wall carbon nanotube producedin Example 3 and 1,4-hydroquinone.

FIG. 13 is a graph showing a change in conductance between a source anda drain with a gate voltage in an electronic device using a carbonnanotube structure constituted by a multi-wall carbon nanotube producedin Example 4 and 1,4-hydroquinone.

FIG. 14 is a graph showing a change in conductance between a source anda drain with a gate voltage in an electronic device using a carbonnanotube structure constituted by a multi-wall carbon nanotube producedin Example 5 and glycerin.

FIG. 15(a) is a schematic sectional diagram of the surface of a basebody for explaining an applied example of the method of manufacturing anelectronic device of the present invention, showing a state afterforming a carbon nanotube structure and patterning it into a shapecorresponding to a transporting layer.

FIG. 15(b) is a schematic sectional diagram of the surface of the basebody for explaining the applied example of the method of manufacturingan electronic device of the present invention, showing a state beforeattachment of a temporary substrate to the substrate shown in FIG.15(a).

FIG. 15(c) is a schematic sectional diagram of the surface of the basebody for explaining the applied example of the method of manufacturingan electronic device of the present invention, showing a state afterattachment of the temporary substrate to the substrate shown in FIG.15(a).

FIG. 15(d) is a schematic sectional diagram of the surface of the basebody for explaining the applied example of the method of manufacturingan electronic device of the present invention, showing a state afterpeeling off the temporary substrate attached to the substrate shown inFIG. 15(a).

FIG. 15(d) is a schematic sectional diagram of the surface of the basebody for explaining the applied example of the method of manufacturingan electronic device of the present invention, showing a state where twotop gate MES-FET's are finally formed at the same time.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an electronic device of the present invention and a methodof manufacturing the same of the present invention will be described.

[Electronic Device]

A transistor, which is a typical active electronic device, is generallycomposed of a source electrode and a drain electrode connected to atransporting layer, and a gate arranged to allow an electric field to beapplied to the transporting layer. A current between the sourceelectrode and the drain electrode is controlled or amplified by applyinga voltage to the gate electrode. In addition, a structure having aninsulating film formed between a gate electrode and a transporting layeris referred to as a MOS-FET (Metal Oxside Semiconductor Field EffectTransistor), which is used for a transistor using silicon for atransporting layer. In addition, a structure having no insulating filmbetween the gate electrode and the transporting layer is referred to asa MES-FET (Metal Semiconductor Field Effect Transistor), which is usedfor a transistor using gallium arsenide for a transporting layer.

A field effect transistor according to an embodiment of the presentinvention has a transporting layer constituted by a carbon nanotubestructure layer having a network structure in which carbon nanotubesmutually cross-link.

An example in which a MOS-FET (metal oxide semiconductor field effecttransistor) thin film transistor, which is an embodiment of the presentinvention, is structured will be described with reference to FIG. 1 andFIG. 2.

FIG. 1 is a side view showing a MOS-FET carbon nanotube transistoraccording to this embodiment, and FIG. 2 is a top view of thetransistor. The carbon nanotube transistor is constituted by a gateelectrode 14, a gate insulating film 13 composed of SiO₂, a transportinglayer 10, a source electrode 15, and a drain electrode 16, which aresequentially laminated on a silicon substrate 11.

The transporting layer 10 is constituted by a carbon nanotube structureformed into a network structure via cross-linked sites in each of whicha plurality of carbon nanotubes cross-link, and each cross-linked siteis formed by chemical bonding. A method of forming the carbon nanotubestructure will be described later. 3 electrodes are arranged on thetransporting layer constituted by a carbon nanotube structure formedinto a network structure via cross-linked sites each formed by chemicalbonding, a current is allowed to flow between the source and the drain,and a gate voltage is applied thereto, with the result that acontrolling effect on the current is exerted.

In addition, a MES-FET (metal semiconductor field effect transistor) maybe adopted as another embodiment of the present invention. FIG. 3 showsa side view of a MES-FET carbon nanotube transistor. FIG. 3 differs fromFIG. 1 in that a transporting layer constituted by the carbon nanotubestructure and a gate electrode are laminated without the gate insulatingfilm 13 interposed between them. Other features are the same as those ofthe MOS-FET, and description thereof will be omitted. Even in thisconfiguration, a current between a source and a drain can be controlledby applying a voltage to a control electrode.

Examples of an available transistor structure include a multigatestructure having a plurality of gate electrodes and a structure in whicha gate electrode is three-dimensionally structured to make an effect ofan electric field on a transporting layer effective. With regard to thearrangement of a gate electrode, any one of various structures such as atop gate structure and a bottom gate structure may be adopted.

(Electrode)

An electrode to be used for the electronic device of the presentinvention has only to be conductive, and examples of such an electrodeinclude: various metal electrodes made of gold, aluminum, copper,platinum, and the like; and electrodes made of organic materials such asconductive polymers. In general, in a semiconductor device using asemiconductor crystal, it may be difficult to form a transporting layeron an electrode owing to the crystal growth. However, the transportinglayer of the present invention is free of such a constraint because itis a carbon nanotube structure. However, from the viewpoint ofwettability of an application solution at the time of application, it ispreferable to select an electrode material in accordance with theapplication solution or to subject the electrode to surface treatmentfor enhancing wettability.

Any one of conventionally used methods can be used as a method offorming an electrode, and examples of the methods include: a methodinvolving deposition by means of a mask; a method involving the use ofphotolithography; and electrodeposition.

A material for a base body is not particularly limited, but in order tocarry a transporting layer of an electronic device, it is preferable touse silicon, a quartz substrate, mica, quartz glass, or the like tofacilitate a patterning process.

However, it may be impossible to pattern a carbon nanotube structurelayer directly on the surface of a base body depending on the shape andnature of the base body. In such a case, it is sufficient that a basebody carrying a patterned carbon nanotube structure layer be attached toa second base body before use, or that a patterned carbon nanotubestructure layer be transferred. By doing so, limitations to be placed ona final substrate carrying an electronic device are mitigated.

In particular, the electronic device of the present invention can beeasily manufactured as described below even when a substrate havingplasticity or flexibility is used as a base body. In addition, thecarbon nanotube structure layer formed on the surface of the base bodyhas a cross-linking structure. Therefore, even if the substrate is bentfor deformation, the carbon nanotube structure layer on the surfacehardly ruptures, with the result that the deterioration of theperformance of the device due to deformation is reduced. In particular,in the case where the carbon nanotube device is used as an electronicdevice, the occurrence of a defect of an electrical path due to bendingis reduced.

Examples of the substrate having plasticity or flexibility includevarious resins such as polyethylene, polypropylene, polyvinyl chloride,polyamide, and polyimide.

<Carbon Nanotube Structure Layer>

In the present invention, the term “carbon nanotube structure layer”refers to a structure formed into a network structure by a plurality ofcarbon nanotubes and cross-linked sites each formed by chemical bondingof different carbon nanotubes. The carbon nanotube structure layer maybe formed according to any method as long as a structure of carbonnanotubes in which carbon nanotubes mutually cross-link through chemicalbonding to construct a network structure can be formed. However, thecarbon nanotube structure is preferably formed according to the methodof manufacturing an electronic device of the present invention to bedescribed later because the structure can be easily manufactured, alow-cost and high-performance transporting layer can be obtained, andthe uniformization and control of characteristics can be easilyperformed.

The carbon nanotube structure to be used as a transporting layer in theelectronic device of the present invention manufactured according to themethod of manufacturing an electronic device of the present invention isobtained by: curing a solution (cross-linking application solution)containing carbon nanotubes having functional groups and a cross-linkingagent which prompts a cross-linking reaction with the functional groups;and subjecting the functional groups of the carbon nanotubes and thecross-linking agent to a cross-linking reaction to form a cross-linkedsite.

Hereinafter, the carbon nanotube structure layer in the electronicdevice of the present invention will be described by taking themanufacturing method as an example.

(Carbon Nanotube) Carbon nanotubes, which are the main component in thepresent invention, may be single-wall carbon nanotubes or multi-wallcarbon nanotubes each having two or more layers. As described above, theinventors of the present invention have found that, when a carbonnanotube structure is formed as in the present invention and is used asa transporting layer, a current controlling effect is exerted bycombination of 3 electrodes regardless of whether each carbon nanotubeis a single-wall carbon nanotube or a multi-wall carbon nanotube.Therefore, Whether one or both types of carbon nanotubes are used (and,if only one type is to be used, which type is selected) or both of themare mixed may be decided appropriately by taking into consideration theuse and characteristics of the electronic device, or the cost.

Carbon nanotubes in the present invention include ones that are notexactly shaped like a tube, such as: a carbon nanohorn (a horn-shapedcarbon nanotube whose diameter continuously increases from one endtoward the other end) which is a variant of a single-wall carbonnanotube; a carbon nanocoil (a coil-shaped carbon nanotube forming aspiral when viewed in entirety); a carbon nanobead (a spherical beadmade of amorphous carbon or the like with its center pierced by a tube);a cup-stacked nanotube; and a carbon nanotube with its circumferencecovered with a carbon nanohorn or amorphous carbon.

Furthermore, carbon nanotubes in the present invention may be ones thatcontain some substances inside, such as: a metal-containing nanotubewhich is a carbon nanotube containing metal or the like; and a peapodnanotube which is a carbon nanotube containing a fullerene or ametal-containing fullerene.

As described above, in the present invention, it is possible to employcarbon nanotubes of any mode, including common carbon nanotubes,variants of common carbon nanotubes, and carbon nanotubes with variousmodifications, without a problem in terms of reactivity. Therefore, theconcept of “carbon nanotube” in the present invention encompasses all ofthe above.

Those carbon nanotubes are conventionally synthesized by a known method,such as arc discharge, laser ablation, and CVD, and the presentinvention can employ any of the methods. However, arc discharge in amagnetic field is preferable from the viewpoint of synthesizing a highlypure carbon nanotube.

Carbon nanotubes used in the present invention are preferably equal toand more than 0.3 nm and equal to or less than 100 nm in diameter. Ifthe diameter of the carbon nanotubes exceeds this range, the synthesisbecomes difficult and costly. A more desirable upper limit of thediameter of the carbon nanotubes is 30 nm or less.

In general, the lower limit of the carbon nanotube diameter is about 0.3nm from a structural standpoint. However, too thin a diameter couldlower the synthesis yield. It is therefore preferable to set the lowerlimit of the carbon nanotube diameter to 1 nm or more, more preferably10 nm or more.

The length of carbon nanotubes used in the present invention ispreferably equal to or more than 0.1 μm and equal to or less than 100μm. If the length of the carbon nanotubes exceeds this range, thesynthesis becomes difficult or requires a special method raising cost,which is not preferable. On the other hand, if the length of the carbonnanotubes falls short of this lower limit, the number of cross-linkbonding points per carbon nanotube is reduced, which is not preferable.A more preferable upper limit of the carbon nanotube length is 10 μm orless and a more preferable lower limit of the carbon nanotube length is1 μm or more.

The appropriate carbon nanotube content in the cross-linking applicationsolution varies depending on the length and thickness of carbonnanotubes, whether single-wall carbon nanotubes or multi-wall carbonnanotubes are used, the type and amount of functional groups in thecarbon nanotubes, the type and amount of cross-linking agents, thepresence or absence of a solvent or other additive used and, if one isused, the type and amount of the solvent or additive, etc. The carbonnanotube content in the solution should be high enough to form anexcellent applied film after curing but not be excessively high becausethe application suitability lowers.

Specifically, the ratio of carbon nanotubes to the entire applicationsolution excluding the mass of the functional groups is in the range ofabout 0.01 to 10 g/l, preferably about 0.1 to 5 g/l, and more preferablyabout 0.5 to 1.5 g/l, although, as mentioned above, the ranges could bedifferent if the parameters are different.

If the purity of carbon nanotubes to be used is not high enough, it isdesirable to raise the purity by prerefining the carbon nanotubes priorto preparation of the cross-linking application solution. In the presentinvention, the higher the carbon nanotube purity, the better the resultcan be. Specifically, the purity is preferably 90% or higher, moredesirably, 95% or higher. When the purity is low, cross-linking agentsare cross-linked to carbon products such as amorphous carbon and tar,which are impurities. This could change the cross-linking distancebetween carbon nanotubes, leading to a failure in obtaining desiredcharacteristics. No particular limitation is put on how carbon nanotubesare refined, and any known conventional refining method can be employed.

(Functional Group) In the present invention, carbon nanotubes can haveany functional group to be connected thereto without particularlimitation, as long as functional groups selected can be added to thecarbon nanotubes chemically and can chemically bond functional groups.

(Functional Group 1)

A preferable first method of forming a cross-linked site is oneinvolving the occurrence of a cross-linking reaction between functionalgroups by means of a certain kind of cross-linking agent. Specificexamples of such functional groups include —COOR, —COX, —MgX, —X (whereX represents halogen), —OR, —NR¹R², —NCO, —NCS, —COOH, —OH, —NH₂, —SH,—SO₃H, —R′CHOH, —CHO, —CN, —COSH, —SR, —SiR′₃ (where R, R¹, R², and R′each independently represent a substituted or unsubstituted hydrocarbongroup). Note that employable functional groups are not limited to thoseexamples.

Of those, it is preferable to use at least one functional group selectedfrom the group consisting of —OH, —COOH, —COOR (where R represents asubstituted or unsubstituted hydrocarbon group), —COX (where Xrepresents a halogen atom), —NH₂, and —NCO. In that case, across-linking agent, which can prompt a cross-linking reaction with theselected functional group, is selected as the cross-linking agent.

In particular, —COOR (where R represents a substituted or unsubstitutedhydrocarbon group) is particularly preferable. This is because acarboxyl group can be relatively easily introduced into a carbonnanotube, because the resultant substance (a carbon nanotube carboxylicacid) can be easily introduced as a functional group by esterifying thesubstance, and because the substance has good reactivity with across-linking agent.

R in the functional group —COOR is a substituted or unsubstitutedhydrocarbon group, and is not particularly limited. However, R ispreferably an alkyl group having 1 to 10 carbon atoms, more preferablyan alkyl group having 1 to 5 carbon atoms, and particularly preferably amethyl group or an ethyl group in terms of reactivity, solubility,viscosity, and ease of use as a solvent of a paint.

The appropriate amount of functional groups introduced varies dependingon the length and thickness of carbon nanotubes, whether single-wallcarbon nanotubes or multi-wall carbon nanotubes are used, the types offunctional groups, the use of the electronic device, etc. From theviewpoint of the strength of the cross-linked substance obtained,namely, the strength of the applied film, a preferable amount offunctional groups introduced is large enough to add two or morefunctional groups to each carbon nanotube.

How functional groups are introduced into carbon nanotubes will beexplained in the section below titled [Method of Manufacturing anElectronic Device].

(Cross-linking Agent)

Any cross-linking agent, which is an essential ingredient of thecross-linking application solution, can be used as long as thecross-linking agent is capable of prompting a cross-linking reactionwith the functional groups of the carbon nanotubes. In other words, thetypes of cross-linking agents that can be selected are limited to acertain degree by the types of the functional groups. Also, theconditions of curing (heating, UV irradiation, irradiation with visiblelight, natural curing, etc.) as a result of the cross-linking reactionare naturally determined by the combination of those parameters.

Specific examples of the preferable cross-linking agents include apolyol, a polyamine, a polycarboxylic acid, a polycarboxylate, apolycarboxylic acid halide, a polycarbodiimide, a polyisocyanate, andhydroquinone. It is desirable to use at least one cross-lining agentselected from the group consisting of the above. In that case, afunctional group which can prompt a cross-linking reaction with thecross-linking agent is selected as the functional group.

At least one functional group and one cross-linking agent areparticularly preferably selected respectively from the group consistingof functional groups exemplified as the preferable functional group andthe group consisting of cross-linking agents exemplified as thepreferable cross-linking agent, so a combination of the functional groupand the cross-linking agent may prompt a cross-linking reaction witheach other. Table 1 below lists the combinations of the functional groupof the carbon nanotubes and the corresponding cross-linking agent, whichcan prompt a cross-linking reaction, along with curing conditions of thecombinations. TABLE 1 Functional group of carbon nanotube Cross-linkingagent Curing condition —COOR Polyol heat curing —COX Polyol heat curing—COOH Polyamine heat curing —COX Polyamine heat curing —OHPolycarboxylate heat curing —OH Polycarboxylic acid heat curing halide—NH₂ Polycarboxylic acid heat curing —NH₂ Polycarboxylic acid heatcuring halide —COOH Polycarbodiimide heat curing —OH Polycarbodiimideheat curing —NH₂ Polycarbodiimide heat curing —NCO Polyol heat curing—OH Polyisocyanate heat curing —COOH Ammonium complex heat curing —COOHHydroquinone heat curing*where R represents a substituted or unsubstituted hydrocarbon group*where X represents a halogen

Of those combinations, preferable is the combination of —COOR (where Rrepresents a substituted or unsubstituted hydrocarbon group) with goodreactivity on a functional group side and a polyol which forms a robustcross-linked substance with ease. The term “polyol” used in the presentinvention is a generic name for organic compounds each having two ormore OH groups. Of those, one having 2 to 10 (more preferably 2 to 5)carbon atoms and 2 to 22 (more preferably 2 to 5) OH groups ispreferable in terms of cross-linkability, solvent compatibiity when anexcessive amount thereof is charged, processability of waste liquidafter a reaction by virtue of biodegradability (environment aptitude),yield of polyol synthesis, and so on. In particular, the number ofcarbon atoms is preferably lower within the above range because a gapbetween carbon nanotubes in the resultant applied film can be narrowedto bring the carbon nanotubes into substantial contact with each other(to bring the carbon nanotubes close to each other). Specifically,glycerin and ethylene glycol are particularly preferable, and it ispreferable to use one or both of glycerin and ethylene glycol as across-linking agent.

Depending on the cross-linking substance to be used, the electricconductivity may reduce owing to an increase in amount of a current usedin the resultant electronic device. For example, a carbon nanotubestructure in which multi-wall carbon nanotubes to which carboxyl groupsare bonded are cross-linked via glycerin shows such a tendency.Therefore, a protective layer for covering a transporting layer ispreferably formed in order to stably use the structure for a long periodof time, or in order to use a large amount of current.

Examples of a material used for a protective layer (passivation layer)for protecting the transporting layer include: existing inorganicmaterials for insulating films and the like such as silicon oxide,silicon nitride, aluminum oxide, and titanium oxide, which are generallyused for a semiconductor device; and insulating organic materials suchas epoxy resins.

In contrast, even if no protective layer is used, when, a cross-linkingagent to be used is, for example, hydroquinone, the absence ofpassivation may show no deterioration. Therefore, it is advantageous touse hydroquinone as a cross-linking agent in terms of long-termstability of characteristics.

From another perspective, the cross-linking agent is preferably anon-self-polymerizable cross-linking agent. Glycerin and ethylene glycolas examples of the polyols are obviously non-self-polymerizablecross-linking agents. More generally, a prerequisite of thenon-self-polymerizable cross-linking agent is to be without a pair offunctional groups, which can prompt a polymerization reaction with eachother, in itself. On the other hand, examples of a self-polymerizablecross-linking agent include one that has a pair of functional groups,which can prompt a polymerization reaction with each other, in itself(alkoxide, for example).

(Functional Group 2)

It is also preferable to adopt a second approach in which a carbonnanotube structure has a network structure in which a plurality ofcarbon nanotubes mutually cross-link via cross-linked sites each formedby chemical bonding of the functional groups at least one end of each ofwhich is connected to a different carbon nanotube.

In this case, carbon nanotubes can have any functional group to beconnected thereto without particular limitation, as long as functionalgroups selected can be added to the carbon nanotubes chemically and canprompt a reaction among the functional groups by means of a certain kindof additive. Specific examples of such functional groups include —COOR,—COX, —MgX, —X (where X represents halogen), —OR, —NR¹R², —NCO, —NCS,—COOH, —OH, —NH₂, —SH, —SO₃H, —R′CHOH, —CHO, —CN, —COSH, —SR, —SiR′₃(where R, R¹, R², and R′ each independently represent a substituted orunsubstituted hydrocarbon group). Note that employable functional groupsare not limited to those examples.

In addition, it is also possible to connect a molecule containing thosefunctional groups in part thereof to a carbon nanotube to cause chemicalbonding at a preferable functional group portion exemplified above. Inthis case as well, a functional group having a large molecular weight tobe bonded to a carbon nanotube is bonded as intended, so the length ofthe cross-linked site can be controlled.

(Additive)

Any additive, which is added to the cross-linking application solution,can be used as long as the additive is capable of prompting a reactionbetween the functional groups of the carbon nanotubes. In other words,the types of additives that can be selected are limited to a certaindegree by the types of the functional groups and the type of thereaction. Also, the conditions of curing (heating, UV irradiation,irradiation with visible light, natural curing, etc.) as a result of thereaction are naturally determined by the combination of thoseparameters.

(Condensation Agent)

Specific preferable examples of the additive include condensation agentssuch as: an acid catalyst; a dehydration condensation agent such assulfuric acid; N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide; anddicyclohexyl carbodiimide. It is preferable to select at least onecondensation agent from the group consisting of the above. In that case,the functional groups, which can prompt a reaction among the functionalgroups with the help of the selected condensation agent, are selected asthe functional groups.

(Base)

Any base, which is an essential ingredient for a substitution reactionin the cross-linking application solution, may be selected depending onthe acidity of a hydroxyl group.

Specific preferable examples of the base include sodium hydroxide,potassium hydroxide, pyridine, and sodium ethoxide. It is preferable toselect at least one base from the group consisting of the above bases.In that case, functional groups, which can prompt a substitutionreaction among the functional groups with the help of the selected base,are selected as the functional groups.

In particular, it is preferable to select at least two functional groupsfrom the group consisting of the functional groups exemplified aspreferable functional groups so that a combination of the selectedfunctional groups is capable of prompting a mutual reaction. Table 2below lists functional groups of carbon nanotubes capable of prompting amutual cross-linking reaction and the names of corresponding reactions.

An additive is not always necessary for an addition reaction. Althoughan additive is not always necessary for an oxidation reaction, anoxidation reaction accelerator is preferably added. An example of theoxidation reaction accelerator that can be suitably added is iodine.TABLE 2 Functional Functional Cross-linked group of carbon group ofcarbon site nanotube(A) nanotube (B) Reaction —COOCO— —COOH —Dehydration condensation —S—S— —SH — Oxidation reaction —O— —OH —Dehydration condensation —NH—CO— —COOH —NH₂ Dehydration condensation—COO— —COOH —OH Dehydration condensation —COO— —COOR —OH Dehydrationcondensation —COO— —COX —OH Dehydration condensation —CH═N— —CHO —NH₂Dehydration condensation —NH— —NH₂ —X Substitution reaction —S— —SH —XSubstitution reaction —O— —OH —X Substitution reaction —O— —OH —OSO₂CH₃Substitution reaction —O— —OH —OSO₂(C₆H₄)CH₃ Substitution reaction—NH—COO— —OH —N═C═O Addition reaction*R represents a substituted or unsubstituted hydrocarbon group*X represents a halogen

The content of a cross-linking agent or an additive for bondingfunctional groups in the cross-linking application solution variesdepending on the type of the cross-linking agent (including whether thecross-linking agent is self-polymerizable or not self-polymerizable) andthe type of the additive for bonding functional groups. The content alsovaries depending on the length and thickness of a carbon nanotube,whether the carbon nanotube is of a single-wall type or a multi-walltype, the type and amount of a functional group of the carbon nanotube,the presence or absence of a solvent or other additives, and, if one isused, the type and amount thereof, and the like. Therefore, the contentcannot be determined uniquely. In particular, for example, glycerin orethylene glycol can also provide characteristics of a solvent because aviscosity of glycerin or ethylene glycol is not so high, and thus anexcessive amount of glycerin or ethylene glycol can be added.

(Other Additive)

The cross-linking application solution may contain various additivesincluding a solvent, a viscosity adjuster, a dispersant, and across-linking accelerator.

A solvent is added when satisfactory application suitability of thecross-linking application solution is not achieved with solely thecross-linking agent or the additive for bonding functional groups. Asolvent that can be employed is not particularly limited, and may beappropriately selected according to the type of the cross-linking agentto be used. Specific examples of employable solvent include: organicsolvents such as methanol, ethanol, isopropanol, n-propanol, butanol,methyl ethyl ketone, toluene, benzene, acetone, chloroform, methylenechloride, acetonitrile, diethyl ether, and tetrahydrofuran (THF); water;aqueous solutions of acids; and alkaline aqueous solutions. A solvent assuch is added in an amount that is not particularly limited butdetermined appropriately by taking into consideration the applicationsuitability of the cross-linking application solution.

A viscosity adjuster is added when satisfactory application suitabilityof the cross-linking application solution is not achieved with solelythe cross-linking agent or the additive for bonding functional groups. Asolvent that can be employed is not particularly limited, and may beappropriately selected according to the type of the cross-linking agentto be used. Specific examples of an employable viscosity adjusterinclude methanol, ethanol, isopropanol, n-propanol, butanol, methylethyl ketone, toluene, benzene, acetone, chloroform, methylene chloride,acetonitrile, diethyl ether, and THF.

Some of those viscosity adjusters have the function of a solvent whenadded in a certain amount, and it is meaningless to apparentlydiscriminate viscosity adjusters from solvents. A viscosity adjuster assuch is added in an amount that is not particularly limited butdetermined appropriately by taking into consideration the applicationsuitability of the cross-linking application solution.

A dispersant is added to the cross-linking application solution in orderto maintain the dispersion stability of the carbon nanotubes or thecross-linking agent, or the additive for bonding functional groups inthe application solution. Various known surface-active agents,water-soluble organic solvents, water, aqueous solutions of acids,alkaline aqueous solutions, etc. can be employed as a dispersant.However, a dispersant is not always necessary since components of thecoating material of the present invention have high dispersion stabilityby themselves. In addition, depending on the use of the applied filmafter the formation, the absence of a dispersant and like otherimpurities in the applied film may be desirable. In such a case, adispersant is not added at all, or is added in a very small amount.

(Method of Preparing the Cross-Linking Application Solution)

A method of preparing a cross-linking application solution is describednext. The cross-linking application solution is prepared by mixingcarbon nanotubes having functional groups with a cross-linking agentthat prompts a cross-linking reaction with the functional groups or anadditive for chemically bonding functional groups as needed (mixingstep). The mixing step may be preceded by an addition step in which thefunctional groups are introduced into the carbon nanotubes.

If carbon nanotubes having functional groups are starting materials, thepreparation is performed simply by the mixing step operation. If normalcarbon nanotubes themselves are starting materials, the preparationstarts with the addition step operation.

The addition step is a step of introducing desired functional groupsinto carbon nanotubes. How functional groups are introduced variesdepending on the type of functional group. One possible method is to adda desired functional group directly, and another possible method is tointroduce a functional group that is easy to attach and then substitutethe whole functional group or a part thereof or attach a differentfunctional group to the former functional group or otherwise in order toobtain the objective functional group.

Still another method is to apply a mechanochemical force to a carbonnanotube to break or modify only a small portion of a graphene sheet onthe surface of the carbon nanotube and introduce various functionalgroups from the broken or modified portion.

Cup-stacked carbon nanotubes, which have many defects on the surfaceupon manufacture, and carbon nanotubes that are formed by vapor phasegrowth are relatively easy to introduce functional groups. On the otherhand, carbon nanotubes each having a perfect graphene sheet structureexert the carbon nanotube characteristics more effectively and areeasier to control the characteristics. Consequently, it is particularlypreferable to use a multi-wall carbon nanotube so that appropriatedefects are as a transporting layer on its outermost layer to bondfunctional groups for cross-linking while the inner layers having lessstructural defects exert the carbon nanotube characteristics.

There is no particular limitation put on the addition step operation andany known method can be employed. Various addition methods described inPatent Document 1 may be employed in the present invention depending onthe purpose.

A description is given on a method of introducing —COOR (where Rrepresents a substituted or unsubstituted hydrocarbon group), aparticularly desirable functional group among the functional groupslisted in the above. To introduce —COOR (where R represents asubstituted or unsubstituted hydrocarbon group) into carbon nanotubes,carboxyl groups may be (i) added to the carbon nanotubes once, and then(ii) esterified.

(i) Addition of Carboxyl Group

To introduce carboxyl groups into carbon nanotubes, carboxyl groups arerefluxed together with an acid having an oxidizing effect. Thisoperation is relatively easy and is preferable since carboxyl groupswith high reactivity are attached to carbon nanotubes. A briefdescription of the operation is given below.

An acid having an oxidizing effect is, for example, concentrated nitricacid, hydrogen peroxide water, a mixture of sulfuric acid and nitricacid, or aqua regia. When concentrated nitric acid is used, inparticular, the concentration is preferably 5 mass % or higher, morepreferably, 60 mass % or higher.

A normal reflux method can be employed. The temperature at which refluxis performed is preferably set to a level near the boiling point of theacid used. When concentrated nitric acid is used, for instance, thetemperature is preferably set to 120 to 130° C. The reflux preferablylasts 30 minutes to 20 hours, more preferably, 1 hour to 8 hours.

Carbon nanotubes to which carboxyl groups are attached (a carbonnanotube carboxylic acid) are generated in the reaction liquid after thereflux. The reaction liquid is cooled down to room temperature and thenreceives a separation operation or washing as necessary, therebyobtaining the objective carbon nanotube carboxylic acid.

(ii) Esterification

The target functional group —COOR (where R represents a substituted orunsubstituted hydrocarbon group) can be introduced by adding an alcoholto the obtained carbon nanotube carboxylic acid and dehydrating themixture for esterification.

The alcohol used for the esterification is determined according to R inthe formula of the functional group. That is, if R is CH₃, the alcoholis methanol, and if R is C₂H₅, the alcohol is ethanol.

A catalyst is generally used in the esterification, and a conventionallyknown catalyst such as sulfuric acid, hydrochloric acid, ortoluenesulfonic acid can also be used in the present invention. The useof sulfuric acid as a catalyst is preferable from a view of notprompting a side reaction in the present invention.

The esterification may be conducted by adding an alcohol and a catalystto a carbon nanotube carboxylic acid and refluxing the mixture at anappropriate temperature for an appropriate time period. A temperaturecondition and a time period condition in this case depend on type of acatalyst, type of alcohol, or the like and cannot be simply determined,but a reflux temperature close to the boiling point of the alcohol usedis preferable. The reflux temperature is preferably in the range of 60to 70° C. for methanol, for example. Further, a reflux time period ispreferably in the range of 1 to 20 hours, more preferably in the rangeof 4 to 6 hours.

A carbon nanotube with the functional group —COOR (where R represents asubstituted or unsubstituted hydrocarbon group) added can be obtained byseparating a reaction product from a reaction solution afteresterification and washing the reaction product as required.

The mixing step is a step of mixing carbon nanotubes having functionalgroups with a cross-linking agent prompting a cross-linking reactionwith the functional groups or an additive for bonding functional groupsas needed, to prepare the cross-linking application solution. In themixing step, other components described in the aforementioned sectiontitled [Wire] are mixed, in addition to the carbon nanotubes havingfunctional groups and the cross-linking agents. Then, preferably, anaddition amount of a solvent or a viscosity adjuster is adjustedconsidering application suitability to prepare the cross-linkingapplication solution just before application to the substrate.

Simple stirring with a spatula and stirring with a stirrer of a stirringblade type, a magnetic stirrer, and a stirring pump may be used for themixing. However, to achieve higher degree of uniformity in dispersion ofthe carbon nanotubes to enhance storage stability while fully extendinga network structure by cross-linking of the carbon nanotubes, anultrasonic disperser or a homogenizer maybe used for powerfuldispersion. However, when using a stirring device with a strong shearforce of stirring such as a homogenizer, there arises a risk of cuttingand damaging the carbon nanotubes in the solution, thus the device maybe used for a very short time period.

A carbon nanotube structure layer is formed by applying a substratesurface with the cross-linking application solution described above andcuring the substrate. An applying method and a curing method aredescribed in detail in the section below titled [Method of Manufacturingan Electronic Device].

The carbon nanotube structure layer in the present invention is in astate where carbon nanotubes are networked. In detail, the carbonnanotube structure layer is cured into a matrix shape, carbon nanotubesare connected to each other via cross-linked sites, and characteristicsof a carbon nanotube itself such as high electron- and hole-transmissioncharacteristics can be exerted sufficiently. In other words, the carbonnanotube structure layer has carbon nanotubes that are tightly connectedto each other, contains no other binders and the like, and is thuscomposed substantially only of carbon nanotubes, so that characteristicsthat are unique of a carbon nanotube are fully utilized.

A thickness of the carbon nanotube structure layer of the presentinvention can be widely selected from being very thin to being thickaccording to an application. Lowering a content of the carbon nanotubesin the cross-linking application solution used (simply, lowering theviscosity by diluting) and applying the cross-linking applicationsolution in a thin coat form allows a very thin applied film to beobtained. Similarly, raising a content of the carbon nanotubes allows athick applied film to be obtained. Further, repeating the applicationallows an even thicker applied film to be obtained. Formation of a verythin applied film from a thickness of about 10 nm is thoroughlypossible, and formation of a thick applied film without an upper limitis possible through recoating. A possible coat thickness with onecoating is about 5 μm.

In the transporting layer constituted by the carbon nanotube structureformed according to the first approach using a cross-linking agent, asite where the carbon nanotubes cross-link together, that is, thecross-linked site formed by a cross-linking reaction between thefunctional groups of the carbon nanotubes and the cross-linking agenthas a cross-linking structure. In the cross-linking structure, residuesof the functional group remaining after a cross-linking reaction areconnected together with a connecting group, which is a residue of thecross-linking agent remaining after a cross-linking reaction.

As described, the cross-linking agent, which is a component of thecross-linking application solution, is preferably notself-polymerizable. If the cross-linking agent is notself-polymerizable, the connecting group of the carbon nanotubestructure layer finally fabricated would be constructed from a residueof only one cross-linking agent. The gap between the carbon nanotubes tobe cross-linked can be controlled to a size of a residue of thecross-linking agent used, thereby providing a desired network structureof the carbon nanotubes with high duplicability. Further, thecross-linking agents are not present between the carbon nanotubes, thusenabling enhancement of an actual density of the carbon nanotubes in thecarbon nanotube structure. Further, reducing a size of a residue of thecross-linking agent can extremely narrow a gap between the carbonnanotubes both electrically and physically (carbon nanotubes aresubstantially in direct contact with each other).

When forming the carbon nanotube structure layer with a cross-linkingapplication solution prepared by selecting a single functional group ofthe carbon nanotubes and a single non-self-polymerizable cross-linkingagent, respectively, the cross-linked site of the layer will have thesame cross-linking structure (Example 1). Further, even when forming thecarbon nanotube structure layer with a cross-linking applicationsolution prepared by selecting multiple types of functional groups ofthe carbon nanotubes and/or multiple types of non-self-polymerizablecross-linking agents, respectively, the cross-linked site of the layerwill mainly have a cross-linking structure based on a combination of thefunctional group and the non-self-polymerizable cross-linking agentmainly used (Example 2).

In contrast, when forming the carbon nanotube structure layer with across-linking application solution prepared by selectingself-polymerizable cross-linking agents, without regard to whether thefunctional groups and the cross-linking agents in the carbon nanotubesare of single or multiple types, the cross-linked site of the layerwhere carbon nanotubes cross-link together will not mainly have aspecific cross-linking structure. This is because the cross-linked sitewill be in a state where numerous connecting groups with differentconnecting (polymerization) numbers of the cross-linking agents coexist.

In other words, by selecting non-self-polymerizable cross-linkingagents, the cross-linked sites of the carbon nanotube structure layerwhere the carbon nanotubes cross-link together bond with the functionalgroup through a residue of only one cross-linking agent, thus forming amainly identical cross-linking structure. “Mainly identical” here is aconcept including a case with all of the cross-linked sites having anidentical cross-linking structure as described above (Example 1), aswell as a case with the cross-linking structure based on a combinationof the functional group and the non-self-polymerizable cross-linkingagent mainly used becomes a main structure with respect to the wholecross-linked site as described above (Example 2).

When referring as “mainly identical”, a “ratio of identical cross-linkedsites” with respect to the whole cross-linked sites will not have auniform lower limit defined. The reason is that a case of imparting afunctional group or a cross-linking structure with an aim different fromformation of a carbon nanotube network maybe assumed, for example, inthe cross-linked sites, for example. However, in order to actualize highelectrical or physical characteristics that are unique of carbonnanotubes with a strong network, a “ratio of identical cross-linkedsites” with respect to the total cross-linked sites is preferably 50% ormore, more preferably 70% or more, further more preferably 90% or more,and most preferably 100%, based on numbers. Those number ratios can bedetermined through, for example, a method of measuring an intensityratio of an absorption spectrum corresponding to the cross-linkingstructure with an infrared spectrum.

As described, if a carbon nanotube structure layer has the cross-linkedsite with a mainly identical cross-linking structure where carbonnanotubes cross-link, a uniform network of the carbon nanotubes can beformed in a desired state. In addition, the carbon nanotube network canbe constructed with homogeneous, satisfactory, and expected electricalor physical characteristics and high duplicability.

Further, the connecting group preferably employs a hydrocarbon as itsskeleton. “Hydrocarbon as its skeleton” here refers to a main chainportion of the connecting group consisting of hydrocarbon, the mainportion of the connecting group contributing to connecting residuestogether of the functional groups of carbon nanotubes to be cross-linkedremaining after a cross-linking reaction. A side chain portion, wherehydrogen of the main chain portion is substituted by anothersubstituent, is not considered. Obviously, it is more preferable thatthe whole connecting group consist of hydrocarbon.

The number of carbon atoms in the hydrocarbon is preferably 2 to 10,more preferably 2 to 5, and further more preferably 2 or 3. Theconnecting group is not particularly limited as long as the connectinggroup is divalent or more.

In the cross-linking reaction of the functional group —COOR (where Rrepresents a substituted or unsubstituted hydrocarbon) and ethyleneglycol, exemplified as a preferable combination of the functional groupof carbon nanotubes and the cross-linking agent, the cross-linked sitewhere the carbon nanotubes mutually cross-link becomes —COO(CH₂)₂OCO—.

Further, in the cross-linking reaction of the functional group —COOR(where R represents a substituted or unsubstituted hydrocarbon) andglycerin, the cross-linked site where the carbon nanotubes mutuallycross-link becomes —COOCH₂CHOHCH₂OCO— or —COOCH₂CH(OCO—)CH₂OH if two OHgroups contribute in the cross-link, and the cross-linked site becomes—COOCH₂CH(OCO—)CH₂OCO— if three OH groups contribute in the cross-link.

In the transporting layer constituted by a carbon nanotube structureformed according to the second approach, functional groups are allowedto react with each other to form a cross-linked site. Therefore, anactual density of the carbon nanotubes in the carbon nanotube structurecan be enhanced. Further, reducing a size of the functional group canextremely narrow a gap between the carbon nanotubes both electricallyand physically, so characteristics of a single carbon nanotube can beeasily exploited. Since a cross-linked site in the nanotube structurelayer in which carbon nanotubes mutually cross-link is formed bychemical bonding of functional groups, the structure is mainly anidentical cross-linking structure. “Mainly identical” here is a conceptincluding a case with all of the cross-linked sites having an identicalcross-linking structure as well as a case with the cross-linkingstructure formed by chemical bonding of the functional groups becomes amain structure with respect to the whole cross-linked site.

As described above, a transporting layer having uniform electricalcharacteristics can be obtained as long as cross-linked sites in each ofwhich carbon nanotubes mutually cross-link are mainly an identicalcarbon nanotube structure.

As described above, the electronic device of the present invention has acarbon nanotube structure in a state where a plurality of carbonnanotubes form a network structure via a plurality of cross-linked siteeach formed by chemical bonding. Therefore, the contact state andarrangement state of carbon nanotubes do not become unstable unlike amere carbon nanotube dispersion film, so electron- and hole-transmissioncharacteristics can be stably exerted. In addition, as described later,the degree of freedom in patterning of the carbon nanotube structurelayer is high, so the transporting layer can have various shapes.

The electronic device of the present invention may have a layer otherthan the carbon nanotube structure layer to be used as a transportinglayer and three or more electrodes. For example, it is preferable tointerpose an adhesive layer between the surface of the base body and thecarbon nanotube structure layer for enhancing adhesiveness between thembecause the adhesive strength of a patterned carbon nanotube structurelayer can be enhanced. A method of forming an adhesive layer and otherdetails will be described in the section titled [Method of Manufacturingan Electronic Device].

Furthermore, a protective layer or any one of other various functionallayers can be placed as an upper layer on the transporting layer of thepatterned carbon nanotube structure. When the protective layer is placedas the upper layer of the transporting layer, the carbon nanotubestructure layer as a network of cross-linked carbon nanotubes can bemore strongly held on the surface of the base body, and can be protectedfrom an external force. A resist layer to be described in the sectiontitled [Method of Manufacturing an Electronic Device] can be usedwithout removal as the protective layer. Of course, newly providing aprotective layer for covering the entire surface including a regionhaving a pattern other than a pattern corresponding to the transportinglayer is effective. Any one of conventionally known various resinmaterials and inorganic materials can be used as a material constitutingsuch a protective layer without any problem depending on purposes.

Furthermore, an integrated circuit can be constituted by formingmultiple electronic devices on the same substrate. In particular,electronic devices using carbon nanotube structures as transportinglayers can be easily integrated by combining: the formation of a carbonnanotube structure layer through application of a solution; and thepatterning.

Alternatively, a highly integrated device can be prepared by: laminatinga transporting layer through the intermediation of an insulating layer;and appropriately connecting carbon nanotube structures between thelayers. The connection between the layers may be performed by separatelyplacing a carbon nanotube structure layer, by using another carbonnanotube, which itself is used as a wiring, or by wiring according toother methods such as the use of a metal film.

In addition, as described above, the base body can be a substrate havingplasticity or flexibility. Using a substrate having plasticity orflexibility as the base body increases the number of applications. Inparticular, the carbon nanotube structure to be used in the presentinvention has a cross-linked site formed by chemical bonding. Therefore,flexibility which a carbon nanotube itself has is effectively exerted,and thus stability against deformation is extremely high even if adevice is constituted by using an electronic device using a substratehaving plasticity or flexibility. Thus, it becomes possible to deal withvarious arrangements, shapes, and usages in a device.

A specific shape and the like of the electronic device of the presentinvention described above will be apparent in the section titled [Methodof Manufacturing an Electronic Device] and the section titled Examples.Of course, the structures to be described later are merelyillustrations, and specific modes of the electronic device of thepresent invention are not limited to these.

[Method of Manufacturing an Electronic Device]

The method of manufacturing an electronic device of the presentinvention is a method suitable for manufacturing the electronic deviceof the present invention described above. Specifically, the methodincludes: (A) a step of applying a solution containing a plurality ofcarbon nanotubes having functional groups (cross-linking applicationsolution) to the surface of a base body; (B) a step of mutuallycross-linking the carbon nanotubes to construct a network structurethrough curing of the cross-linking application solution after theapplication to thereby form a carbon nanotube structure having thenetwork structure; and, in accordance with the structure of anelectronic device to be manufactured, a step of forming an electrodebefore or after the steps (A) and (B).

Furthermore, as required, the method may include another step such as(C) a step of patterning the carbon nanotube structure into a patterncorresponding to the transporting layer.

Hereinafter, the respective steps of a method of manufacturing a MOS-FETcarbon nanotube transistor, which is an embodiment of the presentinvention, will be described with reference to the schematic sectionaldiagrams of FIGS. 4.

(1) and (2) Gate Electrode Forming Step

A substrate 11 the surface of which has been cleansed is prepared andplaced in a deposition apparatus. Then, a metal electrode serving as agate electrode 14 is deposited. As described above, the substrate andthe electrode material can be appropriately selected by takingresistance to subsequent etching or to a subsequent heating process intoconsideration.

(3) Gate Insulating Film Forming Step

In a MOS-FET, a gate insulating film 13 must be formed between the gateelectrode 14 and a transporting layer 10. In the case where an inorganicsemiconductor material such as silicon is used as a transporting layer,a silicon oxide film or a silicon nitride film that tends to form a goodinterface with silicon is used as the gate insulating film in order toprevent an increase in interface state density involved in the surfaceoxidation of a semiconductor crystal. Even in the case where a carbonnanotube structure is used as a transporting layer, an existinginsulating film that can utilize an existing semiconductor process suchas a silicon oxide film, a silicon nitride film, aluminum oxide, ortitanium oxide can be used.

Although the method of forming the gate insulating film 13 depends on amaterial for the film, any one of methods such as application and firingof a MOD (Metal Organic Decomposition) material or deposition can beused.

(4) Supplying Step

In the present invention, the “supplying step” is a step of supplyingthe surface of the base body 11 with a solution 100 (cross-linkingapplication solution) containing the carbon nanotubes having functionalgroups and a cross-linking agent which prompts a cross-linking reactionwith the functional groups. A region with which the cross-linkingapplication solution 100 is to be supplied has only to include thedesired region, and it is not necessary to supply the entire surface ofthe base body 11 with the liquid.

The supplying method, which is preferably application of a cross-linkingsolution, is not particularly limited, and any method can be adoptedfrom a wide range. For example, the liquid may be simply dropped orspread with a squeegee or may be applied by a common application method.Examples of common application methods include spin coating, wire barcoating, cast coating, roll coating, brush coating, dip coating, spraycoating, and curtain coating. The contents of the base body, the carbonnanotubes having functional groups, the cross-linking agent, and thecross-linking application solution are as described in the sectiontitled [Electronic Device]

(5) Cross-Linking Step

In the present invention, the “cross-linking step” is a step of mutuallycross-linking the carbon nanotubes to construct a network structurethrough curing of the cross-linking application solution 100 after theapplication to thereby form a carbon nanotube structure 101. A regionwhere the carbon nanotube structure 101 is to be formed by curing thecross-linking application solution in the cross-linking step has only toinclude the desired region, and it is not necessary to cure the entiretyof the cross-linking application solution 100 applied to the surface ofthe base body.

An operation carried out in the cross-linking step is automaticallydetermined according to the combination of the functional groups withthe cross-linking agent as shown in, for example, Table 1 above. If acombination of thermally curable functional groups is employed, theapplied solution is heated by various heaters or the like. If acombination of functional groups that are cured by ultraviolet rays isemployed, the applied solution is irradiated with a UV lamp or leftunder the sun. If a combination of self-curable functional groups isemployed, it is sufficient to let the applied solution stand still.“Leaving the applied solution to stand still” is deemed as one of theoperations that may be carried out in the cross-linking step of thepresent invention.

For example, heat curing (polyesterification through an ester exchangereaction) is conducted for the case of a combination of a carbonnanotube, to which the functional group —COOR (where R represents asubstituted or unsubstituted hydrocarbon group) is added, and a polyol(among them, glycerin and/or ethylene glycol) Heating causes an esterexchange reaction between —COOR of the esterified carbon nanotubecarboxylic acid and R′—OH (where R′ represents a substituted orunsubstituted hydrocarbon group) of a polyol. As the reaction progressesmultilaterally, the carbon nanotubes are cross-linked until a network ofcarbon nanotubes connected to each other constructs a carbon nanotubestructure layer 14.

To give an example of conditions preferable for the above combination,the heating temperature is specifically set to preferably 50 to 500° C.,more preferably 150 to 200° C., and the heating period is specificallyset to preferably 1 minute to 10 hours, more preferably 1 hour to 2hours.

(6) Patterning Step

In the present invention, the “patterning step” is a step of patterningthe carbon nanotube structure layer into a pattern corresponding to atransporting layer. FIGS. 5(6) to (9) show schematic sectional diagramsshowing (6) Patterning step.

Although no particular limitations are put on operations of thepatterning step, there are two preferred modes of (6-A) and (6-B) to thepatterning step.

(6-A)

A mode in which dry etching is performed on the carbon nanotubestructure layer 101 in a region of the surface of the base body 11 otherthan the region having the pattern corresponding to the transportinglayer, thus removing the carbon nanotube structure layer 101 from theregion and patterning the carbon nanotube structure layer 101 into thepattern corresponding to the transporting layer 10.

Patterning the carbon nanotube structure layer into a patterncorresponding to the transporting layer 10 by dry etching means that thecarbon nanotube structure layer 101 in a region of the surface of thebase body other than the region having the pattern receives irradiationof radicals or the like. Methods of irradiation with radicals or thelike include one in which the carbon nanotube structure layer 101 in aregion other than a region having the pattern is directly irradiatedwith radicals or the like (6-A-1), and one in which the region otherthan a region having the pattern is covered with a resist layer 17 andthen the entire surface of the base body (of course, on the side wherethe carbon nanotube structure layer and the resist layer are formed) isirradiated with radicals or the like (6-A-2).

(6-A-1)

Direct irradiation of the carbon nanotube structure layer 101 in aregion other than a region having the pattern with radicals or the likespecifically means that the carbon nanotube structure layer 101 in aregion of the surface of the base body other than the region having thepattern corresponding to the transporting layer 10 is irradiated with anion of a gas molecule in the form of an ion beam, thereby removing thecarbon nanotube structure layer 101 from the irradiated region andpatterning the carbon nanotube structure layer 101 into a patterncorresponding to the transporting layer 10.

In the form of an ion beam, an ion of a gas molecule can be radiatedselectively with precision on the order of several nm. This method ispreferable in that the carbon nanotube structure layer can be patternedinto a pattern corresponding to a transporting layer in one operation.

Examples of gas species that can be chosen for the ion beam methodinclude oxygen, argon, nitrogen, carbon dioxide, and sulfurhexafluoride. Oxygen is particularly desirable in the present invention.

In the ion beam method, a voltage is applied to gas molecules in avacuum to accelerate and ionize the gas molecules and the obtained ionsare radiated in the form of a beam. The ion beam method is capable ofetching various substances with varying irradiation accuracy by changingthe type of gas used.

(6-A-2)

In the mode in which the regions other than the region having thepattern are covered with a resist layer 17 before the entire surface ofthe base body is irradiated with radicals or the like, the patterningstep includes:

a resist layer forming step (6-A-2-1) of forming a resist layer 17 abovethe carbon nanotube structure layer 101 in a region on the surface ofthe base body having the pattern corresponding to the transportinglayer; and

a removing step (6-A-2-2) of removing the carbon nanotube structurelayer 101 exposed in a region other than the region by subjecting asurface of the base body on which the carbon nanotube structure layer101 and the resist layer 17 are laminated to dry etching. The patterningstep may include:

a resist layer peeling-off step (6-A-2-3) of peeling off the resistlayer 17 formed in the resist layer forming step subsequent to theremoving step.

(6-A-2-1) Resist Layer Forming Step

In the resist layer forming step, the resist layer 17 is formed abovethe carbon nanotube structure layer 101 in a region on the surface ofthe base body having the pattern corresponding to the transporting layer10. This step follows a process generally called a photolithographyprocess and, instead of directly forming a resist layer above the carbonnanotube structure layer in a region having the pattern corresponding tothe transporting layer, the resist layer 17 is once formed on the entiresurface of the base body 11 on the side where the carbon nanotubestructure layer 101 is formed as shown in FIG. 5(6). Then, the regionhaving the pattern corresponding to the transporting layer is exposed tolight and portions that are not exposed to light are removed throughsubsequent development. Ultimately, the resist layer 17 is present onthe carbon nanotube structure layer 101 in the region having the patterncorresponding to the transporting layer.

FIG. 5(7) is a schematic sectional diagram showing a state of thesurface of the base body after (C-A-2-1) resist layer forming step.Depending on the type of resist, a portion that is exposed to light isremoved by development while a portion that is not exposed to lightremains.

A known method can be employed to form the resist layer. Specifically,the resist layer 17 is formed by applying a resist agent to thesubstrate with a spin coater or the like and then heating the appliedagent.

There is no particular limitation on the material (resist agent) used toform the resist layer 17, and various known resist materials can beemployed without any modification. Employing resin (forming a resinlayer) is particularly desirable. The carbon nanotube structure layer101 has a mesh-like network of carbon nanotubes and is a porousstructure. Accordingly, if the resist layer 17 is formed from a metalevaporation film or like other material that forms a film on the verysurface and does not infiltrate deep into the holes of the mesh, carbonnanotubes cannot be sealed satisfactorily against radiation of plasma orthe like (insufficient sealing means exposure to plasma or the like). Asa result, plasma or the like enters from the holes and corrodes thecarbon nanotube layer under the resist layer 17, reducing the contour ofthe remaining carbon nanotube structure layer due to diffraction ofplasma or the like. Although it is possible to give the resist layer 17a larger contour (area) than the pattern corresponding to thetransporting layer, taking into account this reduction in size, thismethod requires a wide gap between patterns and therefore makes itimpossible to form patterns close together.

In contrast, when resin is used to form the resist layer 17, the resinenters the spaces inside the holes and reduces the number of carbonnanotubes that are exposed to plasma or the like. As a result, highdensity patterning of the carbon nanotube structure layer 101 can beperformed.

Examples of the resin material that mainly constitutes the resin layerinclude, but not limited thereto, novolac resin, polymethylmethacrylate, and a mixture of the two.

The resist material for forming the resist layer 17 is a mixture of oneof the above resin materials, or a precursor thereof, and aphotosensitive material or the like. The present invention can employany known resist material. For instance, OFPR 800, a product of TOKYOOHKA KOGYO CO., LTD. and NPR 9710, a product of NAGASE & CO., LTD. canbe employed.

Appropriate operations or conditions to expose the resist layer 17before curing to light (heating if the resist material used is thermallycurable, a different exposure method is chosen for a different type ofresist material) and to develop are selected in accordance with theresist material used. (Examples of exposure and development operationsor conditions include the light source wavelength, the intensity ofexposure light, the exposure time, the exposure amount, environmentalconditions during exposure, the development method, the type andconcentration of developer, the development time, and what pre-treatmentor post-treatment is to be employed.) When a commercially availableresist material is used, the instruction manual for the product shouldbe followed. In general, for conveniences of handling, the layer isexposed to ultraviolet rays to draw the pattern corresponding to thetransporting layer. After that, the film is developed using an alkalinedeveloper, which is then washed off with water, and is let dry tocomplete the photolithography process.

(6-A-2-2) Removing Step

In the removing step, dry etching is performed on a surface of the basebody on which the carbon nanotube structure layer 101 and the resistlayer 17 are laminated, thereby removing the carbon nanotube structurelayer exposed in a region other than the region. (See FIG. 5(7). Thecarbon nanotube structure layer 101 is exposed in a region from whichthe resist layer 17 is removed). FIG. 5(8) is a schematic sectionaldiagram showing a state of the surface of the base body after (6-A-2-2)removing step.

The removing step can employ every method that is generally called dryetching, including the reactive ion method. The above-described ion beammethod in (6-A-1) is one of the dry etching methods.

See the section (6-A-1) for employable gas species, devices, operationenvironments, and the like.

In the present invention, oxygen is particularly desirable out ofexamples of gas species generally usable in dry etching which includeoxygen, argon, and fluorine-based gas (e.g., chlorofluoro carbon, SF₆,and CF₄). With oxygen radicals, carbon nanotubes in the carbon nanotubestructure layer 14 to be removed are oxidized (burnt) and turned intocarbon dioxide. Accordingly, the residue has little adverse effect, andaccurate patterning is achieved.

When oxygen is chosen as gas species, oxygen radicals are generated byirradiating oxygen molecules with ultraviolet rays, and used. A devicethat generates oxygen radicals by means of this method is commerciallyavailable by the name of UV usher, and is easy to obtain.

(6-A-2-3) Resist Layer Peeling-Off Step

The method of manufacturing an electronic device of the presentinvention may shift to (7) Step of forming source and drain electrodesafter the completion of (6-A-2-2) removing step. If the resist layer 17is to be removed, the removing step has to be followed by a resist layerpeeling-off step of peeling off the resist layer 17 formed in the resistlayer forming step. FIG. 5(9) is a schematic sectional diagram showing astate of the surface of the base body after (6-A-2-3) resist layerpeeling-off step.

An appropriate resist layer peeling-off step operation is chosen inaccordance with the material used to form the resist layer 17. When acommercially available resist material is used, the resist layer 17 ispeeled off following the instruction manual for the product. When theresist layer 17 is a resin layer, a common removal method is to bringthe resin layer into contact with an organic solvent that is capable ofdissolving the resin layer.

(6-B)

A mode in which the patterning step includes:

a resist layer forming step of forming a resist layer above the carbonnanotube structure layer in a region on the surface of the base bodyhaving the pattern corresponding to the transporting layer; and

a removing step of removing the carbon nanotube structure layer exposedin a region other than the region by bringing a surface of the base bodyon which the carbon nanotube structure layer and the resist layer arelaminated into contact with an etchant.

The mode is a method commonly called wet etching (a method of removingan arbitrary portion using chemical=etchant).

The resist layer forming step in Mode (C-B) is identical with (6-A-2-1)resist layer forming step described above except that a resist materialhaving resistance to the etchant should be used in Mode (C-B). Similarto Mode (C-A) patterning step, the removing step in Mode (C-B)patterning step may be followed by the resist layer peeling-off step anddetails of this peeling-off step are as described in (6-A-2-3) resistlayer peeling-off step. Detailed descriptions of these steps aretherefore omitted here.

Reference is made to FIG. 5(7). In the removing step, an etchant isbrought into contact with the surface of the base body 11 on which thecarbon nanotube structure layer 101 and the resist layer 17 arelaminated, thereby removing the carbon nanotube structure layer 101exposed in a region other than the region.

In the present invention, “bringing an etchant into contact with” is aconcept including all operations for bringing a liquid into contact witha subject, and a liquid may be brought into contact with a subject byany methods such as dipping, spraying, and letting a liquid flow over asubject.

The etchant is in general an acid or alkali. Which etchant to choose isdetermined by the resist material constituting the resist layer 17, thecross-linking structure among carbon nanotubes in the carbon nanotubestructure layer 101, and other factors. A desirable etchant is one thatetches the resist layer 17 as little as possible and that can easilyremove the carbon nanotube structure layer 10.1.

However, an etchant that etches the resist layer 17 may be employed ifit is possible to, by appropriately controlling the temperature andconcentration of the etchant and how long the etchant is in contact withthe carbon nanotube structure layer, remove the exposed carbon nanotubestructure layer 101 before the resist layer 17 is completely etchedaway.

(7) Step of Forming Source and Drain Electrodes

In the same manner as in the (2) gate electrode forming step, a sourceelectrode 15 and a drain electrode 16 are arranged on the remainingcarbon nanotube structure layer 101, which functions as the transportinglayer 10, so as to be opposed to each other with a gap between theelectrodes. FIG. 5(10) shows a schematic sectional diagram showing astate of the surface of the base body after the step. Materials for theelectrodes are identical with the case of the gate electrode, and arepreferably selected by taking wettability with respect to the gateinsulating film/the carbon nanotube structure layer into consideration.

As described above, in the case of a bottom gate, a gate electrode isformed first as in the description of this embodiment. In contrast, inthe case of a top gate, the step of forming source and drain electrodesis performed first.

(8) Other Steps

The electronic device of the present invention can be manufacturedthrough the above steps. However, the method of manufacturing anelectronic device of the present invention may include additional steps.

For instance, it is preferable to put a surface treatment step forpre-treatment of the surface of the base body before the applying step.The purpose of the surface treatment step is, for example, to enhancethe absorption of the cross-linking application solution to be applied,to enhance the adhesion between the surface of the base body and thecarbon nanotube structure layer to be formed thereon as an upper layer,to clean the surface of the base body, or to adjust the electricconductivity of the surface of the base body.

An example of surface treatment for enhancing the absorption of thecross-linking application solution is treatment by a silane couplingagent (e.g., aminopropyltriethoxysilane orγ-(2-aminoethyl)aminopropyltrimethoxysilane). Surface treatment byaminopropyltriethoxysilane is particularly widely employed and ispreferable for the surface treatment step in the present invention. Asdocumented by Y. L. Lyubchenko et al. in “Nucleic Acids Research vol. 21(1993)“on pages 1117 to 1123, for example, surface treatment byaminopropyltriethoxysilane has conventionally been employed to treat thesurface of a mica substrate for use in observation of AFM of DNA.

In the case where two or more carbon nanotube structure layers are to belaminated, the operation of the method of manufacturing an electronicdevice of the present invention is repeated twice or more. If anintermediate layer such as a dielectric layer or an insulating layer isto be interposed between carbon nanotube structure layers, a step forforming the layer is inserted in between and then the operation of themethod of manufacturing an electronic device of the present invention isrepeated.

In the case where a plurality of electronic devices of the presentinvention are juxtaposed and integrated on a substrate, the plurality ofelectronic devices are produced in tandem in the respective patterningsteps and interconnection is established between a device and anotherdevice or an element such as a resistor or a capacitor to form acircuit.

In addition, in the case where other layers such as a protective layerand an electrode layer are separately laminated, a step for formingthese layers is needed. Each of those layers may be appropriately formedby selecting the material and forming method for the layer depending ona purpose from conventionally known ones or by using a product or methodnewly developed for the present invention.

<Applied Example of Method of Manufacturing an Electronic Device of thePresent Invention>

An applied example of the method of manufacturing an electronic deviceof the present invention is, for example, a method involving the stepsof: patterning a carbon nanotube structure layer on the surface of atemporary substrate; and transferring the patterned carbon nanotubestructure layer on to a desired base body. In addition, in thetransferring step, the patterned carbon nanotube structure layer may betransferred from the temporary substrate to the surface of anintermediate transfer body and then to a desired base body (second basebody).

A specific method of forming a MES-FET carbon nanotube transistor, whichis an embodiment of the present invention, will be described withreference to FIGS. 15.

In the same manner as that described above, a carbon nanotube structureis formed on a temporary substrate 11′, and is patterned into a shapecorresponding to the transporting layer 10 (FIG. 15(a)). In thisexplanation, two transporting layers were simultaneously formed on thetemporary substrate.

Subsequently, a substrate 11 on which an adhesive surface 111 has beenformed is attached to the transporting layer 10 on the temporarysubstrate 11′ (FIGS. 15(b) and (c)).

The substrate 11 and the temporary substrate 11′ are peeled off of eachother, whereby the transporting layer 10 is transferred onto thesubstrate 11 (FIG. 15(d)).

Subsequently, the gate electrode 14, the source electrode 15, and thedrain electrode 16 are formed by means of sputtering or the like on thetransporting layer 10 transferred onto the substrate 11.

Thus, two top gate MES-FET's are simultaneously formed (FIG. 15(e)).

The temporary substrate material that can be used in this appliedexample is preferably the same as the base body material described inthe section titled [Electronic Device]. However, a temporary substratethat has at least one flat surface, more desirably, one that is shapedlike a flat plate is preferable in consideration of transfer suitabilityin the transferring step.

To be employable in the applied example, a base body or an intermediatetransfer body has to have an adhesive surface holding, or capable ofholding, an adhesive. Common tape such as cellophane tape, paper tape,cloth tape, or imide tape can be of course used in the applied example.In addition to the tape and other materials that have plasticity orflexibility, rigid materials may also be employed as a base body or anintermediate transfer body. In the case of a material that does not comewith an adhesive, an adhesive is applied to a surface of the materialthat can hold an adhesive, and then the material can be used in asimilar fashion to normal adhesive tape.

According to the applied example, the electronic device of the presentinvention can be easily manufactured.

An electronic device can also be manufactured by: preparing a base bodyin a state where a carbon nanotube structure layer is carried on thesurface of the base body; and attaching the base body to a surface of adesired second base body (for example, a casing) on which 3 electrodesfor constituting the electronic device have been formed.

Alternatively, even when the user skips the cross-linking step, atransporting layer of an electronic device can be also manufactured by:using a carbon nanotube transfer body in which a carbon nanotubestructure layer is carried on the surface of a temporary substrate (orintermediate transfer body) to transfer only the carbon nanotubestructure layer onto the surface of a base body constituting theelectronic device; and removing the temporary substrate (or intermediatetransfer body). Here, the intermediate transfer body may serve as atemporary substrate of the carbon nanotube transfer body during theprocess. However, there is no need to distinguish the intermediatetransfer body from the carbon nanotube transfer body itself, and hencethe case is also included in the present invention. The electronicdevice can be formed by forming the 3 electrodes on the substrate inadvance or by forming them after the removal of the temporary substrate.

The use of a carbon nanotube transfer body extremely simplifies thesubsequent handling because a carbon nanotube structure layer in across-linked state is carried on the surface of a temporary substrate.Therefore, the manufacture of an electronic device can be performed withextreme ease. A method of removing a temporary substrate can beappropriately selected from simple peeling, chemical decomposition,burnout, melting, sublimation, dissolution, and the like.

The applied example of the method of manufacturing an electronic deviceis particularly effective in the case where a base body of a device hasa material and/or shape that make it difficult to apply the method ofmanufacturing an electronic device of the present invention without somechanges.

For instance, the applied example of the present invention is effectivein the case where the temperature at which the solution after theapplication is cured in the cross-linking step is equal to or higherthan the melting point or glass transition point of the material that isto be used as a base body of the device. In this case, the heatingtemperature is set lower than the melting point of the temporarysubstrate to ensure a heating temperature necessary for the curing, andthus the electronic device of the present invention can be manufacturedappropriately.

To give another example, the applied example of the present invention iseffective also when the patterning step takes a mode in which dryetching is performed on the carbon nanotube structure in a region of thesurface of the temporary substrate other than the region having thepattern corresponding to the transporting layer, thus removing thecarbon nanotube structure layer in the region and patterning the carbonnanotube structure into a pattern corresponding to the transportinglayer while the material that is to be used as a base body of theelectronic device has no resistance to dry etching of the patterningstep. In this case, a material having resistance to dry etching is usedas the temporary substrate so that the resistance to the operation ofthe step of patterning on the temporary substrate can be ensured, andthus the electronic device of the present invention can be manufacturedappropriately.

Although specifics on resistance, material, and the like vary dependingon dry etching conditions including gas species, intensity, time,temperature, and pressure, resin materials have relatively lowresistance to dry etching. When a resin material is used as the basebody, limitations brought by low resistance of the resin material arelifted by employing this applied example. Therefore, forming the basebody from a resin material is preferable in that merits of the appliedexample are brought out. On the other hand, inorganic materials whichhave relatively high resistance to dry etching are suitable for thetemporary substrate. In general, plastic or flexible materials have lowresistance to dry etching and therefore using one of such materials asthe base body is preferable in that merits of this applied example arebrought out.

To give another example, the applied example of the present invention iseffective also in the case where the patterning step includes: a resistlayer forming step of forming a resist layer above the carbon nanotubestructure layer in a region on the surface of the temporary substratehaving the pattern corresponding to the transporting layer; and aremoving step of removing the carbon nanotube structure layer exposed ina region other than the region by bringing a surface of the temporarysubstrate on which the carbon nanotube structure layer and the resistlayer are laminated into contact with an etchant, and the base body hasno resistance to the etchant used in the patterning step, but thetemporary substrate has resistance to the etchant. In this case, a basebody of the electronic device serves as the base body in this appliedexample and a material having resistance to the etchant is used as thetemporary substrate, so the resistance to the operation of the step ofpatterning onto the temporary substrate can be ensured. Thus, theelectronic device of the present invention can be manufacturedappropriately.

Specifics on resistance and material vary depending on etchingconditions including the type, concentration, and temperature of theetchant used, how long the etchant is in contact with the carbonnanotube structure layer, and the like. When an acidic etchant is usedand a base body of the electronic device is to be formed from aluminumor like other materials that do not withstand acid, for example,limitations brought by low resistance of the base body material arelifted by employing the applied example and using silicon or othermaterials having resistance to acid as the temporary substrate.Limitations brought by low resistance are also lifted by using as thebase body a material that has low resistance to an etchant as describedabove although depending on whether the etchant is acidic or alkaline.

As another mode, for making the electronic device of the presentinvention easy to handle even more, a base body that carries the carbonnanotube structure may be pasted onto a second base body to constitutethe electronic device of the present invention or an apparatus using thesame. The second base body may be physically rigid or may be plastic orflexible, and can take various shapes including a spherical shape and aconcave-convex shape.

<More Specific Example>

A more specific description of the present invention is given belowthrough Examples. However, the present invention is not limited to thefollowing examples.

EXAMPLE 1

A MOS-FET carbon nanotube transistor was manufactured through a flow ofthe method of manufacturing an electronic device shown in FIGS. 4 and 5.It should be noted that reference numerals in FIGS. 4 and 5 may be usedin the description of this example.

(A) Applying Step (A-1) Preparation of Cross-Linking ApplicationSolution (Adding Step)

(i) Purification of Single-Wall Carbon Nanotube

Single-wall carbon nanotube powder (purity 40%, manufactured bySigma-Aldrich Co.) was sifted through a sieve (125 μm in pore size) inadvance to remove a coarse agglomerate. 30 mg of the remainder (havingan average diameter of 1.5 nm and an average length of 2 μm) were heatedat 450° C. for 15 minutes by using a muffle furnace, and then a carbonsubstance other than a carbon nanotube was removed. 15 mg of theremaining powder were immersed in 10 ml of a 5-N aqueous solution ofhydrochloric acid {prepared by diluting concentrated hydrochloric acid(a 35% aqueous solution, manufactured by KANTO KAGAKU) with pure waterby a factor of 2} to dissolve a catalyst metal.

The solution was filtered to collect a precipitate. The collectedprecipitate was subjected to the heating step 3 times and the step ofimmersing in hydrochloric acid 3 times for purification. At that time,conditions for heating were gradually made more severe: 450° C. for 20minutes, then 450° C. for 30 minutes, and then 550° C. for 60 minutes.

The carbon nanotube after the purification is found to show a remarkableincrease in purity as compared to that before the purification (rawmaterial) (more specifically, the purity is estimated to be 90% orhigher). The finally obtainedpurified carbon nanotube had a mass (1 to 2mg) of about 5% of the mass of the raw materials.

The above operation was repeated a number of times to purify 15 mg ormore of high-purity single-wall carbon nanotube powder.

(ii) Addition of Carboxyl Group . . . Synthesis of Carbon NanotubeCarboxylic Acid

30 mg of multi-wall carbon nanotube powder (purity: 90%, averagediameter: 30 nm, average length: 3 μm, manufactured by ScienceLaboratory Inc.) were added to 20 ml of concentrated nitric acid (a 60mass % aqueous solution, manufactured by KANTO KAGAKU) for reflux at120° C. for 5 hours to synthesize a carbon nanotube carboxylic acid. Areaction scheme of the above is shown in FIG. 6. In FIG. 6, a carbonnanotube (CNT) is represented by two parallel lines (same applies forother figures relating to reaction schemes).

The temperature of the solution was returned to room temperature and thesolution was subjected to centrifugal separation at 5,000 rpm for 15minutes to separate supernatant liquid from precipitate. The recoveredprecipitate was dispersed in 10 ml of pure water, and the dispersionliquid was subjected to centrifugal separation again at 5,000 rpm for 15minutes to separate supernatant liquid from precipitate (the aboveprocess constitutes one washing operation). This washing operation wasrepeated five more times and lastly precipitate was recovered.

An infrared absorption spectrum of the recovered precipitate wasmeasured. An infrared absorption spectrum of the used multi-wall carbonnanotube raw material itself was also measured for comparison. Acomparison between both the spectra revealed that absorption at 1,735cm⁻¹ characteristic of a carboxylic acid, which was not observed in thesingle-wall carbon nanotube raw material itself, was observed in theprecipitate. This finding shows that a carboxyl group was introducedinto a carbon nanotube by the reaction with nitric acid. In other words,this finding confirmed that the precipitate was a carbon nanotubecarboxylic acid.

Addition of the recovered precipitate to neutral pure water confirmedthat dispersability was good. This result supports the result of theinfrared absorption spectrum that a hydrophilic carboxyl group wasintroduced into a carbon nanotube.

(iii) Esterification

30 mg of the carbon nanotube carboxylic acid prepared in the above stepwere added to 25 ml of methanol (manufactured by Wako Pure ChemicalIndustries, Ltd.). Then, 5 ml of concentrated sulfuric acid (98 mass %,manufactured by Wako Pure Chemical Industries, Ltd.) were added to themixture, and reflux was conducted at 65° C. for 6 hours for methylesterification. The reaction scheme for the above-mentioned methylesterification is shown in FIG. 7.

After the temperature of the solution had been recovered to roomtemperature, the solution was filtered to separate a precipitate. Theprecipitate was washed with water, and was then recovered. An infraredabsorption spectrum of the recovered precipitate was measured. As aresult, absorption at 1,735 cm⁻¹ and that in the range of 1,000 to 1,300cm⁻¹ characteristic of ester were observed. This result confirmed thatthe carbon nanotube carboxylic acid was esterified.

(Mixing step)

30 mg of the carbon nanotube carboxylic acid methyl esterified in theabove step were added to 4 g of glycerin (manufactured by KANTO KAGAKU)and the whole was mixed using an ultrasonic disperser. Further, themixture was added to 4 g of methanol as a viscosity adjuster to preparea cross-linking application solution (100).

(A-2) Surface Treatment Step of Base Body

Prepared was a silicon wafer having a silicon oxide film on its surfacefor insulation (manufactured by Advantech Co., Ltd, 76.2 mmΦ (diameterof 3 inches), thickness of 380 μm, thickness of a surface oxide film of1 μm) as the base body 11. An aluminum thin film was deposited as thegate electrode 14 on the wafer. The silicon oxide insulating film 13 wasformed on the gate electrode 14 by using a MOD coating material ofsilicon oxide (manufactured by JAPAN PURE CHEMICAL CO., LTD.). The widthof the gate electrode was set to 2,000 μm.

The silicon wafer was subjected to surface treatment using amino propyltriethoxysilane for enhancing adsorption of the silicon wafer withrespect to the cross-linking application solution (100) to be applied tothe wafer.

The silicon wafer was subjected to the surface treatment usingaminopropyltriethoxysilane by exposing the silicon wafer to steam of 50μl of aminopropyltriethoxysilane (manufactured by Sigma-Aldrich Co.) forabout 3 hours in a closed Schale.

For comparison, a silicon wafer which had not been subjected to surfacetreatment was also separately prepared.

(A-3) Applying Step

The cross-linking application solution 100 (1 μl) prepared in Step (A-1)was applied to the surface of the silicon wafer subjected to the surfacetreatment by using a spin coater (1H-DX2, manufactured by MIKASA Co.,Ltd.) at 100 rpm for 30 seconds. The solution was similarly applied tothe silicon wafer for comparison which had not been subjected to thesurface treatment.

(B) Cross-Linking Step

After the application of the cross-linking application solution 100, thesilicon wafer (base body 11) on which the applied film had been formedwas heated at 200° C. for 2 hours to cure the applied film, therebyforming the carbon nanotube structure layer 101 (FIG. 4(5)). FIG. 8shows the reaction scheme.

The observation of the state of the obtained carbon nanotube structurelayer 101 by means of an optical microscope confirmed an extremelyuniform cured film.

(C) Patterning Step

(C-1) Resist Layer Forming Step

A resist agent 170 (manufactured by Nagese & Co., LTD, NPR9710,viscosity of 50 mPa·s) was applied to the surface on the side of thecarbon nanotube structure layer 101 of the silicon wafer 12 (subjectedto surface treatment) on which the carbon nanotube structure layer 101had been formed by using a spin coater (manufactured by Mikasa, 1H-DX2)at 2,000 rpm for 20 seconds. Then, the applied agent was heated at 100°C. for 2 minutes to form a film, thereby forming the resist layer 17(FIG. 5(6)).

The resist agent NPR9710 had the following composition.

-   -   Propylene glycol monomethyl ether acetate: 50 to 80 mass %    -   Novolac resin: 20 to 50 mass %    -   Photosensitive agent: less than 10 mass %

The surface on the side of the resist layer 17 of the silicon wafer 11on which the carbon nanotube structure layer 101 and the resist layer 17had been formed was exposed to light to have a shape corresponding tothe transporting layer 10 to be used for a MOS-FET under the conditionof a light amount of 12.7 mW/cm² for 8 seconds by using a mask aligner(mercury vapor lamp manufactured by Mikasa, MA-20, wavelength of 436nm).

Furthermore, the exposed silicon wafer 11 was heated on a hot plate at110° C. for 1 minute. Then, the silicon wafer was left to stand to cool,and development was performed on a developing machine (AD-1200, TakizawaIndustries) by using as a developer NMD-3 manufactured by TOKYO OHKAKOGYO CO., LTD. (tetramethyl ammonium hydroxide 2.38 mass %) (FIG.5(7)). At this time, an optical microscope was used to confirm that theresist layer 17 was formed into a shape of the transporting layer 10.

(C-2) Removing Step

The silicon wafer 11 on which the resist layer 17 had been thus formedinto the shape of the predetermined pattern was heated in a mixed gas(oxygen 10 mL/min, nitrogen 40 mL/min) at 200° C. and irradiated withultraviolet rays (172 nm) for 2 hours by using a UV usher (excimervacuum ultraviolet lamp, manufactured by Atom Giken, EXM-2100BM,wavelength of 172 nm) to generate oxygen radicals, thereby removing aportion of the carbon nanotube structure layer 101 which was notprotected by the resist layer 17. As a result, the carbon nanotubestructure layer 101 was formed into the shape of the transporting layer10 in a state of being covered with the resist layer 17 (FIG. 5(8)).

The resist layer 17 remains on the surface of the base body 11 throughthe carbon nanotube structure layer 101.

(C-3) Resist Layer Peeling-Off Step

The resist layer 17 remaining as an upper layer of the carbon nanotubestructure layer 10 formed into the shape of the “predetermined pattern”was removed by washing it with acetone (FIG. 5(9)) to obtain atransporting layer of an electronic device of Example 1.

Gold was deposited on the transporting layer as the source electrode 15and the drain electrode 16 to obtain a MOS-FET carbon nanotube fieldeffect transistor shown in FIG. 1 (FIG. 5(10)). The gap between thesource electrode 15 and the drain electrode was set to 1,000 μm.

Next, a semiconductor parameter analyzer 4156B (manufactured by AgilentTechnologies) was used to measure direct current-voltage characteristicsfor a current between the source and drain electrodes with respect to avoltage Vgs of the gate electrode. FIG. 10 shows the result. The resultconfirmed that the carbon nanotube structure serves as the transportinglayer because the conductivity between the drain and source electrodeschanges with the gate voltage.

EXAMPLE 2

A MES-FET carbon nanotube field effect transistor shown in FIG. 3 wasproduced in the same manner as in Example 1 except that the insulatingfilm forming step was omitted. At this time, the gate electrode widthand the distance between the source and drain electrodes were set to 500μm and 1,500 μm, respectively. Then, the field effect transistor wassubjected to measurement by means of a parameter analyzer 4156B(manufactured by Agilent Technologies) in the same manner as in Example1 to confirm a change in electric conductivity between the source andthe drain with the gate voltage Vgs. The result confirmed that thecurrent between the source and the drain can be controlled by the gatevoltage (FIG. 11).

EXAMPLE 3

A carbon nanotube structure was formed by using a cross-linkingapplication solution using a multi-wall carbon nanotube, and a MOS-FETcarbon nanotube field effect transistor shown in FIG. 1 was produced inthe same manner as in Example 1. A method of forming an applied filmwill be shown below. The other steps were the same as those of Example1.

(A) Applying Step

(A-1) Preparation of Cross-Linking Application Solution (Addition Step)

(i) Addition of Carboxyl Group . . . Synthesis of Carbon NanotubeCarboxylic Acid

30 mg of multi-wall carbon nanotube powder (purity: 90%, averagediameter: 30 nm, average length: 3 μm, manufactured by ScienceLaboratory Inc.) were added to 20 ml of concentrated nitric acid (a 60mass % aqueous solution, manufactured by KANTO KAGAKU) for reflux at120° C. for 20 hours to synthesize a carbon nanotube carboxylic acid.

The temperature of the solution was returned to room temperature and thesolution was subjected to centrifugal separation at 5,000 rpm for 15minutes to separate supernatant liquid from precipitate. The recoveredprecipitate was dispersed in 10 ml of pure water, and the dispersionliquid was subjected to centrifugal separation again at 5,000 rpm for 15minutes to separate supernatant liquid from precipitate (the aboveprocess constitutes one washing operation). This washing operation wasrepeated five more times and lastly precipitate was recovered.

An infrared absorption spectrum of the recovered precipitate wasmeasured. An infrared absorption spectrum of the used multi-wall carbonnanotube raw material itself was also measured for comparison. Acomparison between both the spectra revealed that absorption at 1,735cm⁻¹ characteristic of a carboxylic acid, which was not observed in themulti-wall carbon nanotube raw material itself, was observed in theprecipitate. This finding shows that a carboxyl group was introducedinto a carbon nanotube by the reaction with nitric acid. In other words,this finding confirmed that the precipitate was a carbon nanotubecarboxylic acid.

Addition of the recovered precipitate to neutral pure water confirmedthat dispersability was good. This result supports the result of theinfrared absorption spectrum that a hydrophilic carboxyl group wasintroduced into a carbon nanotube.

(Mixing Step)

5 mg of the carbon nanotube carboxylic acid obtained in the above stepand 30 mg of 1,4-hydroquinone (manufactured by Wako Pure ChemicalIndustries, Ltd.) were added to 20 ml of dimethylformamide (manufacturedby Wako Pure Chemical Industries, Ltd.), and the whole was further mixedwith N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide (hydrochloride,manufactured by Sigma-Aldrich Co.) using an ultrasonic disperser. 30 mgof the carbon nanotube carboxylic acid methyl esterified in the abovestep were added to 4 g of glycerin (manufactured by KANTO KAGAKU), andthe whole was mixed using an ultrasonic disperser. Further, the mixturewas added to 4 g of methanol as a viscosity adjuster to prepare across-linking application solution (1). FIG. 9 shows the reactionscheme.

Next, a semiconductor parameter analyzer 4156B (manufactured by AgilentTechnologies) was used to measure direct current-voltage characteristicsfor a current between the source and drain electrodes with respect to avoltage of the gate electrode (FIG. 12).

The result confirmed that the electric conductivity between the sourceand drain electrodes can be changed with the gate voltage Vgs, and thatthe carbon nanotube structure using a multi-wall carbon nanotube servesas the transporting layer.

EXAMPLE 4

A MES-FET electronic device shown in FIG. 3 was produced by using acarbon nanotube structure using a multi-wall carbon nanotube in the samemanner as in Example 3 except that the insulating film forming step inExample 3 was omitted. Next, a semiconductor parameter analyzer 4156B(manufactured by Agilent Technologies) was used to measure directcurrent-voltage characteristics for a current between the source anddrain electrodes with respect to a voltage of the gate electrode (FIG.13).

The result confirmed that the carbon nanotube structure serves as thetransporting layer because the conductivity between the drain and sourceelectrodes changes with the gate voltage.

EXAMPLE 5

A carbon nanotube structure was formed by using a cross-linkingapplication solution using a multi-wall carbon nanotube, and a MOS-FETsemiconductor device shown in FIG. 1 was produced in the same manner asin Example 3. A mixing step for the cross-linking application solutiondifferent from Example 3 will be explained.

(Mixing Step)

30 mg of the carbon nanotube carboxylic acid methyl esterified in theabove step were added to 4 g of glycerin (manufactured by KANTO KAGAKU),and the whole was mixed using an ultrasonic disperser. Further, themixture was added to 4 g of methanol as a viscosity adjuster to preparea cross-linking application solution (1).

Next, a semiconductor parameter analyzer 4156B (manufactured by AgilentTechnologies) was used to measure direct current-voltage characteristicsfor a current between the source and drain electrodes with respect to avoltage of the gate electrode. The result confirmed that the carbonnanotube structure can be used as the transporting layer because theconductivity between the drain and source electrodes changes with thegate voltage (FIG. 14).

1. An electronic device, characterized by comprising: three or moreelectrodes; and a transporting layer constituted by a carbon nanotubestructure formed into a network structure by a plurality of carbonnanotubes and cross-linked sites each constituted by chemical bonding ofthe different carbon nanotubes, in which a carrier is transported inaccordance with a voltage applied to the electrodes.
 2. An electronicdevice according to claim 1, characterized in that the electrodescomprise at least a source electrode, a drain electrode, and a gateelectrode to constitute a field effect transistor structure.
 3. Anelectronic device according to claim 2, characterized in that the fieldeffect transistor structure comprises a MOS-FET structure.
 4. Anelectronic device according to claim 2, characterized in that the fieldeffect transistor structure comprises a MES-FET structure.
 5. Anelectronic device according to 4 claim 1, characterized in that, in thecarbon nanotube structure layer, the carbon nanotubes for connectionbetween cross-linked sites of the carbon nanotubes comprise mainlysingle-wall carbon nanotubes.
 6. An electronic device according to 4claim 1, characterized in that, in the carbon nanotube structure layer,the carbon nanotubes for connection between cross-linked sites of thecarbon nanotubes comprise mainly multi-wall carbon nanotubes.
 7. Anelectronic device according to claim 1, characterized in that chemicalbonds constituting the cross-linked sites comprise at least one chemicalbond selected from the group consisting of (—COO(CH₂₎ ₂OCO—),—COOCH₂CHOHCH₂OCO—, —COOCH₂CH(OCO—)CH₂OH, —COOCH₂CH(OCO—)CH₂OCO—, and—COO—C₆H₄—COO—.
 8. An electronic device according to claim 1,characterized in that the chemical bonds constituting the cross-linkedsites comprise at least one chemical bond selected from the groupconsisting of —COOCO—, —O—, —NHCO—, —COO—, —NCH—, —NH—, —S—, —O—,—NHCOO—, and —S—S—.
 9. An electronic device according to claim 1,characterized in that the carbon nanotube structure is obtained by usinga solution containing a plurality of carbon nanotubes to whichfunctional groups are bonded and forming a cross-linked site throughchemical bonding of the functional groups bonded to the carbonnanotubes.
 10. An electronic device according to claim 9, characterizedin that the carbon nanotube structure is obtained by curing a solutioncontaining carbon nanotubes having functional groups and a cross-linkingagent that prompts a cross-linking reaction with the functional groups,prompting a cross-linking reaction between each of the functional groupsbonded to the different carbon nanotubes and the cross-linking agent,and forming a cross-linked site.
 11. An electronic device according toclaim 10, characterized in that the cross-linking agent comprises anon-self-polymerizable cross-linking agent.
 12. An electronic deviceaccording to claim 10, characterized in that the functional groupscomprise at least one group selected from the group consisting of —OH,—COOH, —COOR (where R represents a substituted or unsubstitutedhydrocarbon group), —COX (where X represents a halogen atom), —NH₂, and—NCO, and the cross-linking agent comprises a cross-linking agent whichmay prompt a cross-linking reaction with the selected functional groups.13. An electronic device according to claim 10, characterized in thatthe cross-linking agent comprises at least one cross-linking agentselected from the group consisting of a polyol, a polyamine, apolycarboxylic acid, a polycarboxylate, a polycarboxylic acid halide, apolycarbodiimide, a polyisocyanate, and hydroquinone, and the functionalgroups comprise functional groups which may prompt a cross-linkingreaction with the selected cross-linking agent.
 14. An electronic deviceaccording to claim 10, characterized in that: the functional groupscomprise at least one group selected from the group consisting of —OH,—COOH, —COOR (where R represents a substituted or unsubstitutedhydrocarbon group), —COX (where X represents a halogen atom), —NH₂, and—NCO; the cross-linking agent comprises at least one cross-linking agentselected from the group consisting of a polyol, a polyamine, apolycarboxylic acid, a polycarboxylate, a polycarboxylic acid halide, apolycarbodiimide, a polyisocyanate, and hydroquinone; and the functionalgroups and the cross-linking agent are respectively selected in such amanner that combination of the functional groups and the cross-linkingagent may prompt a cross-linking reaction with each other.
 15. Anelectronic device according to claim 9, characterized in that thecross-linked sites are constituted by chemical bonding of the functionalgroups.
 16. An electronic device according to claim 15, characterized inthat reactions for causing the chemical bonding comprise at least oneselected from the group consisting of dehydration condensation, asubstitution reaction, an addition reaction, and an oxidation reaction.17. An electronic device according to claim 1, characterized in that thetransporting layer is obtained by patterning the carbon nanotubestructure into a shape corresponding to a formation area of thetransporting layer.
 18. An electronic device according to claim 1,characterized by comprising a flexible substrate on which the electrodeand the transporting layer are formed.
 19. An integrated circuit,characterized by comprising: a substrate; and a plurality of electronicdevices each of which is described in claim 1, the electrodes beingintegrated on the substrate.
 20. A method of manufacturing an electronicdevice that includes, on a base body, three or more electrodes and atransporting layer in which a carrier is transported in accordance witha voltage applied to the electrodes, characterized by comprising: asupplying step of supplying the base body with a solution containing aplurality of carbon nanotubes to which functional groups are bonded; anda cross-linking step of chemically bonding the functional groups,constructing a network structure in which the carbon nanotubes mutuallycross-link, and forming a carbon nanotube structure used as thetransporting layer.
 21. A method of manufacturing an electronic deviceaccording to claim 20, characterized in that the supplying stepcomprises an applying step of applying the solution onto the base body,and the carbon nanotube structure is of a film shape.
 22. A method ofmanufacturing an electronic device according to claim 20, characterizedin that the carbon nanotubes comprise mainly single-wall carbonnanotubes.
 23. A method of manufacturing an electronic device accordingto claim 20, characterized in that the carbon nanotubes comprise mainlymulti-wall carbon nanotubes.
 24. A method of manufacturing an electronicdevice according to claim 20, characterized in that the solutioncontains a cross-linking agent for cross-linking the functional groups.25. A method of manufacturing an electronic device according to claim24, characterized in that the cross-linking agent comprises anon-self-polymerizable cross-linking agent.
 26. A method ofmanufacturing an electronic device according to claim 24, characterizedin that the functional groups comprise at least one group selected fromthe group consisting of —OH, —COOH, —COOR (where R represents asubstituted or unsubstituted hydrocarbon group), —COX (where Xrepresents a halogen atom), —NH₂, and —NCO, and the cross-linking agentcomprises a cross-linking agent which may prompt a cross-linkingreaction with the selected functional groups.
 27. A method ofmanufacturing an electronic device according to claim 24, characterizedin that the cross-linking agent comprises at least one cross-linkingagent selected from the group consisting of a polyol, a polyamine, apolycarboxylic acid, a polycarboxylate, a polycarboxylic acid halide, apolycarbodiimide, a polyisocyanate, and hydroquinone, and the functionalgroups comprise functional groups which may prompt a cross-linkingreaction with the selected cross-linking agent.
 28. A method ofmanufacturing an electronic device according to claim 24, characterizedin that: the functional groups comprise at least one group selected fromthe group consisting of —OH, —COOH, —COOR (where R represents asubstituted or unsubstituted hydrocarbon group), —COX (where Xrepresents a halogen atom), —NH₂, and —NCO; the cross-linking agentcomprises at least one cross-linking agent selected from the groupconsisting of a polyol, a polyamine, a polycarboxylic acid, apolycarboxylate, a polycarboxylic acid halide, a polycarbodiimide, apolyisocyanate, and hydroquinone; and the functional groups and thecross-linking agent are respectively selected in such a manner thatcombination of the functional groups and the cross-linking agent mayprompt a cross-linking reaction with each other.
 29. A method ofmanufacturing an electronic device according to claim 24, characterizedin that the functional groups are comprise —COOR (where R represents asubstituted or unsubstituted hydrocarbon group).
 30. A method ofmanufacturing an electronic device according to claim 29, characterizedin that the cross-linking agent comprises a polyol.
 31. A method ofmanufacturing an electronic device according to claim 30, characterizedin that the cross-linking agent comprises glycerin and/or ethyleneglycol.
 32. A method of manufacturing an electronic device according toclaim 20, characterized in that a reaction for causing the chemicalbonding comprises a reaction for chemically bonding the functionalgroups.
 33. A method of manufacturing an electronic device according toclaim 32, characterized in that the solution contains an additive forcausing the chemical bonding of the functional groups.
 34. A method ofmanufacturing an electronic device according to claim 33, characterizedin that the reaction comprises dehydration condensation and the additivecomprises a condensation agent.
 35. A method of manufacturing a carbonnanotube structure according to claim 34, characterized in that thefunctional groups comprise at least one selected from —COOR (where Rrepresents a substituted or unsubstituted hydrocarbon group), —COOH,—COX (where X represents a halogen atom), —OH, —CHO, and —NH₂.
 36. Amethod of manufacturing an electronic device according to claim 35,characterized in that the functional groups comprise —COOH.
 37. A methodof manufacturing an electronic device according to claim 34,characterized in that the condensation agent comprises at least onecompound selected from the group consisting of sulfuric acid,N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide, and dicyclohexylcarbodiimide.
 38. A method of manufacturing an electronic deviceaccording to claim 33, characterized in that the reaction comprises asubstitution reaction and the additive comprises a base.
 39. A method ofmanufacturing an electronic device according to claim 38, characterizedin that the functional groups comprise at least one group selected fromthe group consisting of —NH₂, —X (where X represents a halogen atom),—SH, —OH, —OSO₂CH₃, and —OSO₂(C₆H₄)CH₃.
 40. A method of manufacturing anelectronic device according to claim 38, characterized in that the basecomprises at least one compound selected from the group consisting ofsodium hydroxide, potassium hydroxide, pyridine, and sodium ethoxide.41. A method of manufacturing an electronic device according to claim32, characterized in that the reaction comprises an addition reaction.42. A method of manufacturing an electronic device according to claim41, characterized in that the functional groups comprise —OH and/or—NCO.
 43. A method of manufacturing an electronic device according toclaim 32, characterized in that the reaction comprises an oxidationreaction.
 44. A method of manufacturing an electronic device accordingto claim 43, characterized in that the functional groups comprise —SH.45. A method of manufacturing an electronic device according to claim43, characterized in that the solution contains an oxidation reactionaccelerator.
 46. A method of manufacturing an electronic deviceaccording to claim 45, characterized in that the oxidation reactionaccelerator comprises iodine.
 47. A method of manufacturing anelectronic device according to claim 20, characterized in that thesolution further contains a solvent.
 48. A method of manufacturing anelectronic device according to claim 24, characterized in that thecross-linking agent serves also as a solvent.
 49. A method ofmanufacturing an electronic device according to claim 20, characterizedby comprising a patterning step of patterning the carbon nanotubestructure layer into a shape corresponding to the transporting layer.50. A method of manufacturing an electronic device according to claim49, characterized in that the patterning step comprises a stepinvolving: subjecting a carbon nanotube structure layer in a regionhaving a pattern other than a pattern corresponding to the transportinglayer on a surface of the base body to dry etching to remove the carbonnanotube structure layer in the region; and patterning the carbonnanotube structure layer into the pattern corresponding to thetransporting layer.
 51. A method of manufacturing an electronic deviceaccording to claim 49, characterized in that the patterning stepcomprises: a resist layer forming step of forming a resist layer on thecarbon nanotube structure layer in the region having the patterncorresponding to the transporting layer on the surface of the base body;and a removing step of removing a carbon nanotube structure layerexposed in a region other than the region by subjecting a surface of thebase body on which the carbon nanotube structure layer and the resistlayer are laminated to dry etching.
 52. A method of manufacturing anelectronic device according to claim 51, characterized in that, in theremoving step, the surface of the base body on which the carbon nanotubestructure layer and the resist layer are laminated is irradiated with aradical of an oxygen molecule.
 53. A method of manufacturing anelectronic device according to claim 52, characterized in that an oxygenradical is generated by irradiating an oxygen molecule with ultravioletlight, the oxygen radical being used as the radical with which thesurface of the base body on which the carbon nanotube structure layerand the resist layer are laminated is irradiated.
 54. A method ofmanufacturing an electronic device according to claim 51, characterizedin that the patterning step further includes, subsequent to the removingstep, a resist layer peeling-off step of peeling off the resist layerformed in the resist layer forming step.
 55. A method of manufacturingan electronic device according to claim 54, characterized in that theresist layer comprises a resin layer.
 56. A method of manufacturing anelectronic device according to claim 50, characterized in that thepatterning step comprises a step involving: selectively irradiating thecarbon nanotube structure layer in the region having a pattern otherthan the pattern corresponding to the transporting layer on the surfaceof the base body with an ion of a gas molecule in a form of an ion beamto remove the carbon nanotube structure layer in the region; andpatterning the carbon nanotube structure layer into the patterncorresponding to the transporting layer.